Method and apparatus for purifying polluted substances containing halogenated organic compound

ABSTRACT

A nutrient solution is reduced with a reducing agent, and introduced into a contaminated object. Alternatively, groundwater reduced with a reducing agent is introduced into the contaminated object. Groundwater is contacted with the reducing agent while being circulated between an aquifer and a housing. A nutrient source for heterotrophic anaerobic microorganism may also be introduced into the contaminated object. The contaminated object contaminated with halogenated organic compounds can be purified efficiently and easily.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a purification method and apurification apparatus capable of effectively purifying a contaminatedobject containing halogenated organic compounds. More particularly, theinvention relates to a purification method and a purification apparatuscapable of purifying a contaminated object containing chlorinatedorganic compounds, such as soil, sediment, sludge, or water, e.g.,interstitial water of sludge or groundwater, by a chemical reaction or areductive dehalogenation reaction comprising a combination of a chemicalreaction and a biological reaction, to degrade the halogenated organiccompounds efficiently.

RELATED ART

The entire disclosure of an international application PCT/JP/98/00363,filed with the Japanese Patent Office on Jan. 29, 1998, entitled “AMethod for Purifying Object Contaminated with Halogenated OrganicCompounds,” is cited in the present patent application.

In recent years, there have been one report after another oncontamination of soil and groundwater with halogenated organiccompounds, such as tetrachloroethylene, trichloroethylene,1,1,1-trichloroethane, and dichloroethylene, which are widely used asdegreasing agents for metal components of electronic equipment, andcleaning agents for dry cleaning. Recently, in particular, attention hasbeen attracted to contamination with dioxins discharged fromincineration facilities, PCB, etc. These halogenated organic compoundsare not easily degraded in the natural world, and sparingly soluble inwater. Thus, they tend to be accumulated in the soil and penetrated intogroundwater in the contaminated area. The halogenated organic compoundsare also known to cause hepatic damage and have carcinogenicity. It isdesired, therefore, that halogenated organic compounds, such aschlorinated organic compounds, contained in the soil, etc. be degradedand rendered harmless.

Recently, bioremediation has attracted attention as a method ofpurifying soil, groundwater, etc. contaminated with halogenated organiccompounds. The bioremediation method is highly cost-effective and hashigh safety. Bioremediation, however, has the problems that treatmentrequires a long time, and the types and concentrations of substanceswhich can be degraded are restricted, as will be described below.

Aerobic degradation of trichloroethylene by methane assimilatingorganisms, toluene or phenol degrading organisms, ammonia oxidizingbacteria, or alkene assimilating organisms is known as an example ofbioremediation. However, this method has the following drawbacks: 1)Degradation reaction is unstable. 2) The scope of substances to bedegraded is very narrow. 3) It has no degrading action on highlychlorinated substances such as tetrachloroethylene and carbontetrachloride.

Many anaerobic microorganisms, on the other hand, can degrade highlychlorinated organic compounds, such as tetrachloroethylene,trichloroethylene, and carbon tetrachloride, and have a broad range ofapplications. However, they are defective, for example, in that 1)growth of the microorganisms is very slow, and 2) strongly toxicintermediary metabolites are formed and accumulated during the anaerobicdegradation process (Uchiyama HIROO and Yagi OSAMI, Bioscience andIndustry, 1994, Vol. 52, No. 11, 879-884).

As a technique for decomposing halogenated organic compounds by achemical reaction, reductive treatment of chlorinated organic compoundswith metallic iron has been reported (Yazaki TETSUO, Treatment ofOrganochlorine Compound Contaminated Groundwater—Technology forTreatment at Low Temperatures with Metallic Iron Deposited ActivatedCarbon, “PPM”, 1995, Vol. 26, No. 5, 64-70). Thus, the inventor of thepresent invention attempted to conduct dechlorination experiments byadding metallic iron into the soil in the absence of a carbon source formicroorganisms. However, no dechlorination reaction was observed underconditions under which no microorganisms were cultured, particularlywhen a reductive atmosphere and neutral conditions were not maintained.Nor was any dechlorination reaction noted when an iron salt, such asFeCl₂, FeCl₃ or FeSO₄, was added instead of metallic iron.

Furthermore, there is a report of a method for treating halogenatedorganic compounds to become harmless, which comprises injecting metalliciron and high pressure air into contaminated soil to react thehalogenated organic compounds with an iron powder to make it inorganic(Japanese Unexamined Patent Publication No. 1996-257570). This methodinvolves a problem about air injection facilities, and a risk ofvaporization of the halogenated organic compounds. The method is alsoimpractical, since the use of high pressure air causes the problem ofcost.

There is also a report of a method for removing organochlorinecompounds, which have contaminated soil or groundwater, by combining anatural substance having a dehalogenation catalytic action andbioremediation (“Nikkei Biotech” (Nikkei BP), published Oct. 7, 1996,No. 361, 14-15). However, this report is silent on concrete naturalsubstances and microorganisms.

U.S. Pat. No. 5,411,664 describes a method for degradation ofhalogenated organic compounds by addition of a fibrous organic materialand polyvalent metal particles, e.g., iron, to a contaminated object.However, this U.S. patent does not describe a reducing agent, such asreduced iron, cast iron, an alloy, or a water-soluble reducing agent.Nor does this patent describe that the contaminated object is held in areducing atmosphere after addition of a reducing agent.

In the laboratory, it is easy to mix a reducing agent, a nutrientsource, and a contaminated object uniformly. To purify a contaminatedobject, such as soil, actually in situ, on the other hand, large amountsof a reducing agent and a nutrient source are mixed, thus requiringconstruction work. Moreover, uniform mixing is not necessarily easy. Inaddition, the conditions during kneading may affect the degradationratio of halogenated organic compounds. To purify a contaminated objectof a volume of 1 m³ or more, particularly, a volume of 10 m³ or more, aningenious idea is needed for the kneading method.

Besides, to purify a contaminated object, such as soil, in situ, it hasbeen common practice to perform a small amount of pumping downstreamfrom a contaminated aquifer, apply purification treatment for thecontaminated object to the pumped groundwater, then dissolve a nutrientsource for microorganisms, which degrade the contaminant, in the treatedgroundwater, and inject the groundwater again into an upstreamunsaturated soil or aquifer. With this method, however, the pumpedcontaminated water cannot be reinjected unless it is purified below theconcentration complying with the ban on the permeation of effluent intothe ground. Thus, it is necessary to install purification facilities onthe ground, posing the problem of an increased cost. Also, the injectednormal water brings about a phenomenon of a detour formed in the flow ofthe contaminated groundwater. This phenomenon poses the problem that theinjected nutrient source does not thoroughly mix with the groundwater.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide acontaminated object purification method and purification apparatus whichcan efficiently and easily purify a contaminated object containinghalogenated organic compounds. Particularly, its object is to provide apurification method and a purification apparatus which can efficientlyand easily purify a contaminated object containing halogenated organiccompounds, especially soil and groundwater, in situ.

According to one aspect of the present invention, water is circulated soas to pass through the contaminated object, for example, thecontaminated object in the soil. According to another aspect of thepresent invention, circulation of water in this manner is not required.

According to an aspect of the present invention, there is provided apurification method for purifying a contaminated object containinghalogenated organic compounds, including a reduction step in which areducing agent having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of from 300 mV to −2400 mVreduces a nutrient solution containing a nutrient source forheterotrophic anaerobic microorganisms and water, and an introductionstep in which the reduced nutrient solution is introduced into thecontaminated object after the reduction step. Preferably, theintroduction step is performed after, preferably immediately after, thereduction step.

The purification method according to this aspect of the presentinvention combines a chemical reaction and a biodegradation reaction,and can degrade the halogenated organic compounds to purify thecontaminated object containing the halogenated organic compounds. Byintroducing the reduced nutrient solution into the contaminated objectafter, preferably immediately after, the reduction step, the reducedstate of the nutrient solution can be maintained, and the activity ofthe microorganism can be enhanced to purify the contaminated object moreefficiently. Here, “immediately after the reduction step” refers to“after a lapse of a sufficiently short time to maintain the reducedstate of the nutrient solution.”

In the introduction step, a well, an underground wall, a permeationgutter, a trench, or an indentation is preferably used.

The reduction step preferably includes a contact step of bringing thenutrient solution into contact with the reducing agent which is in asolid state and is insoluble or sparingly soluble in water.

Alternatively, the reduction step preferably includes a mixing step ofmixing the nutrient solution with an aqueous solution containing thereducing agent which is water soluble.

In the introduction step, the reduced nutrient solution is preferablyintroduced into the contaminated object via a deep indentation providedin the ground surface, for example, a well, or an underground wall. Inthe ground with high permeability, however, the reduced nutrientsolution may be introduced via a shallow indentation.

It is preferred to further have a step of circulating groundwatercontaining the halogenated organic compounds and provide the reductionstep and the introduction step while circulating the groundwater.

Herein, the halogenated organic compounds refer to fluorinated organiccompounds, chlorinated organic compounds, brominated organic compounds,or iodinated organic compounds. Particularly, the invention is targetedat, but not limited to, aliphatic compounds such as tetrachloroethylene,trichloroethylene, 1,1,1-trichloroethane or dichloroethylene, andaromatic compounds such as pentachlorophenol, which present problems ascontamination sources for groundwater and soil.

The contaminated object includes, for example, groundwater, soil,sediment, sludge, compost, manured organic substances, waste, anddrainage.

The ratio between the nutrient source for the heterotrophic anaerobicmicroorganisms and water that are contained in the nutrient solution isnot restricted. The nutrient source for the heterotrophic anaerobicmicroorganisms can be selected, as desired, according to the propertiesof the microorganisms in the contaminated object to be purified.

Preferred examples of the heterotrophic anaerobic microorganisms aremethane-forming bacteria (e.g., the genus Methanosarcina, the genusMethanothrix, the genus Methanobacterium, the genus Methanobrevibacter),sulfate-reducing bacteria (e.g., the genus Desulfovibrio, the genusDesulfotomaculum, the genus Desulfobacterium, the genus Desulfobacter,the genus Desulfococcus), nitrate-reducing bacteria (e.g., the genusBacillus, the genus Lactobacillus, the genus Aeromonas, the genusStreptococcus, the genus Micrococcus), acid-forming bacteria (e.g., thegenus Clostridium, the genus Acetivibrio, the genus Baceroides, thegenus Ruminococcus), and facultative anaerobic bacteria (e.g., the genusBacillus, the genus Lactobacillus, the genus Aeromonas, the genusStreptococcus, the genus Micrococcus). Particularly, the generaBacillus, Pseudomonas, Aeromonas, Streptococcus and Micrococcus arepreferred, because they have oxide form nitrogen reducing activity.

Examples of the nutrient source which can be used preferably when theheterotrophic anaerobic microorganisms are methane-forming bacteria areshown in Tables 1 and 2 below.

TABLE 1 Culture medium for methane-forming microorganisms ConstituentFormulation Tap water 800 ml Mineral 1 solution* 50 ml/l Mineral 2solution* 50 ml/l Trace mineral solution* 10 ml/l Trace vitaminsolution* 10 ml/l NaHCO₃ 5.0 g/l Yeast Extract 1.0 g/l Polypeptone 20g/l Glucose 25 g/l Sodium citrate 25 g/l Methanol 50 ml/l L-cysteinehydrochloride solution 5.0 ml/l Na₂S.9H₂O solution 5.0 ml/l pH 6.9-7.2

The mineral 1 solution refers to a solution containing 6 g of K₂HPO₄ in1 liter of distilled water.

The mineral 2 solution refers to a solution containing 6 g of KH₂PO₄, 6g of (NH₄)₂SO₄, 12 g of NaCl, 2.6 g of MgSO₄.7H₂O, and 0.16 g ofCaCl₂.2H₂O in 1 liter of distilled water.

The trace mineral solution refers to a solution containing 1.5 g ofnitrilotriacetic acid, 3.0 g of MgSO₄.7H₂O, 0.5 g of MnSO₄ 2H₂O, 1.0 gof NaCl, 0.1 g of FeSO₄.7H₂O, 0.1 g of CoSO₄ or CoCl₂, 0.1 g ofCaCl₂.2H₂O, 0.1 g of ZnSO₄, 0.01 g of CuSO₄.5H₂O, 0.01 g of AlK(SO₄)₂,0.01 g of H₃BO₃, and 0.01 g of Na₂MoO₄.2H₂O in 1 liter of distilledwater. First, nitrilotriacetic acid is dissolved while being adjusted topH 6.5 with KOH, and then the other minerals are added. Finally, thesolution is adjusted to pH 7.0 with KOH.

The trace vitamin solution refers to a solution containing 2 mg ofbiotin, 2 mg of folic acid, 10 mg of pyridoxine hydrochloride, 5 mg ofthiamine hydrochloride, 5 mg of riboflavin, 5 mg of nicotinic acid, 5 mgof calcium DL-pantothenate, 0.1 mg of vitamin B₁₂, 5 mg ofp-aminobenzoic acid, and 5 mg of lipoic acid in 1 liter of distilledwater.

TABLE 2 Culture medium for methane-forming microorganisms ConstituentAmount L-cysteine hydrochloride 0.1 g/l Polypeptone 2.0 g/l Glucose 2.5g/l Sodium citrate 2.5 g/l Methanol 5.0 ml/l Sodium bicarbonate 5.0 g/lSodium sulfide nonahydrate 0.1 g/l Yeast extract 1.0 g/l Dilution waterTap water pH 6.9-7.2

An example of the nutrient source which can be used preferably when theheterotrophic anaerobic microorganisms are sulfate-reducing bacteria isshown in Table 3 below.

TABLE 3 Culture medium for sulfate-reducing microorganisms ConstituentFormulation Tap water 1000 ml K₂HPO₄ 0.5 g/l NH₄Cl 1.0 g/l Na₂SO₄ 1.0g/l CaCl₂.2H₂O 0.1 g/l MgSO₄.7H₂O 2.0 g/l Yeast Extract 1.0 g/lFeSO₄.7H₂O 0.2 g/l Trace vitamin solution* 10 ml/l Sodium lactate 25ml/l Sodium acetate 25 ml/l Sodium thioglycolate 0.1 g/l Ascorbic acid0.1 g/l pH 6.6-7.0 *The trace vitamin solution is the same as the tracevitamin solution in Table 1.

An example of the nutrient source which can be used preferably when theheterotrophic anaerobic microorganisms are nitrate-reducing bacteria isshown in Table 4 below.

TABLE 4 Culture medium for nitrate-reducing microorganisms ConstituentAmount Potassium nitrate 4.5 g/l Potassium acetate 8.5 g/l Sodiumbicarbonate 5.0 g/l Magnesium chloride hexahydrate 0.2 g/l Yeast extract0.1 g/l Dilution water Tap water pH 6.9-7.4

The use of organic carbon and a culture medium, which contains 20 to 50%by weight of organic carbon, preferably 20 to 30% by weight of oxideform nitrogen, as the nutrient source is preferred, because themicroorganism population involved in the aforementioned chemicalreaction and biological reaction can be changed to suppress blackeningof the soil due to iron sulfide, etc., occurrence of a methane gas, andgeneration of foul-smelling gases such as mercaptan. Furthermore, anitrogen gas is generated, producing the advantage that the resultinghydrogen gas is diluted. The oxide form nitrogen is preferably in theform of a nitrate. A preferred example of the nitrate is an alkali metalsalt of nitric acid, an alkaline earth metal salt of nitric acid, ironnitrate, titanium nitrate, manganese nitrate, aluminum nitrate, ormagnesium nitrate. Particularly, sodium nitrate, potassium nitrate orcalcium nitrate can be used preferably. The organic carbon is preferablya water soluble organic carbon source. Preferred examples of the organiccarbon source are sugars, organic acids or their derivatives, loweralcohols, molasses waste liquor, fermentation waste liquor, and mixturesof them.

In connection with the reducing agent used in the present invention, itsstandard electrode potential, relative to a standard hydrogen electrodeat 25° C., of higher than 300 mV is not preferred, because a sufficientreducing power is not obtained. The standard electrode potential of lessthan −2400 mV is not preferred, either, because the reducing power is sostrong that a hydrogen gas may be generated, posing a danger. Thestandard electrode potential (E°) relative to a standard hydrogenelectrode at 25° C. is shown in Table 5.

TABLE 5 Standard electrode potential (E °) relative to a standardhydrogen electrode at 25° C. Electrode reaction E ° (mV) Ca²⁺ + 2e⁻ Ca−2865 Na⁺ + e⁻ Na −2714 Mg²⁺ + 2e⁻ Mg −2363 Al³⁺ + 3e⁻ Al −1662 Zn²⁺ +2e⁻ Zn −763 Fe²⁺ + 2e⁻ Fe −440 Cd²⁺ + 2e⁻ Cd −403 Ni²⁺ + 2e⁻ Ni −250Sn²⁺ + 2e⁻ Sn −136 2H⁺ + 2e⁻ H₂ 0 Ascorbic acid (ph 7.0) 58 CO₃ ²⁻ +3H⁺ + 2e⁻ HCOO⁻ + H₂O 311 2CO₃ ²⁻ + 4H⁺ + 2e⁻ C₂O₄ ²⁻ + 2H₂O 478 Au³⁺ +3e⁻ Au 1520

As the reducing agent, a reducing agent which is in a solid state and isinsoluble or sparingly soluble in water, or a water soluble reducingagent can be used preferably.

As the reducing agent in solid state, there can be preferably cited atleast one reducing agent selected from the group consisting of reducediron, cast iron, iron-silicon alloy, titanium alloy, zinc alloy,manganese alloy, aluminum alloy, magnesium alloy, calcium alloy,titanium-silicon alloy, titanium-aluminum alloy, zinc-aluminum alloy,manganese-magnesium alloy, aluminum-zinc-calcium alloy, aluminum-tinalloy, aluminum-silicon alloy, and calcium-silicon alloy.

When reduced iron is used as the solid state reducing agent, adsorptionof the halogenated organic compounds to the surface of the reduced ironoccurs. Simultaneously, polarization into an anode and a cathode takesplace on the surface of the reduced iron because of the difference inconditions between the metal side and the environment side to flow anelectric current. Accordingly, iron solves out as iron ions on the anodeas shown in the following formula 1, and electrons flow into thecathode, causing a reduction reaction:

Fe→Fe²⁺+2e⁻  Formula 1

When cast iron is used as the reducing agent, graphite contained in thecast iron adheres to the surface. This graphite acts as a cathode, whilethe iron acts as an anode. When the alloy is used as the reducing agent,polarization into an anode and a cathode occurs according to thestandard electrode potentials of the metallic elements making up thealloy. In the case of the alloy, a reducing atmosphere can be maintainedmore easily, and the potential difference from the halogenated organiccompounds becomes greater. Thus, a dehalogenation reaction is promoted.

When the reducing agent in a solid state and insoluble or sparinglysoluble in water is used as the reducing agent, it is preferred for thereducing step to include a contact step of contacting the nutrientsolution with the reducing agent. Inclusion of the contact step permitsa thorough reaction between the reducing agent insoluble or sparinglysoluble in water and the nutrient solution, leading to reduction of thenutrient solution.

As the solid state reducing agent, a powder having a particle size of500 μm or less can be cited preferably.

As the water soluble reducing agent, there can be preferably named anorganic acid or its derivative, hypophosphorous acid or its derivative,or a salt of an organic acid or hypophosphorous acid with iron,titanium, zinc, manganese, aluminum or magnesium, or a sulfide salt.

As the organic acid, a carboxylic acid, a sulfonic acid, a phenolicacid, or a derivative thereof can be cited preferably. Preferredexamples of the carboxylic acid are monocarboxylic acids, dicarboxylicacids, tricarboxylic acids and tetracarboxylic acids having 1 to 20carbon atoms and optionally substituted by hydroxyl groups. Concretely,acetic acid, citric acid and terephthalic acid are preferred, andaliphatic tricarboxylic acids having 2 to 10 carbon atoms, such ascitric acid, are particularly preferred. As the derivative of thephenolic acid, a polyhydroxyaryl can be named preferably. As thepolyhydroxyaryl, 1,2,3-trihydroxybenzene and 1,4-dihydroxybenzene arepreferred. As the derivatives of the organic acid, salts, esters,amides, and acid anhydrides can be preferably cited.

As the derivatives of hypophosphorous acid, salts and esters can becited preferably, and salts are particularly preferred.

The use of the water soluble reducing agent, compared with the use ofthe reducing agent in solid state, dramatically increases the efficiencyof contact with the halogenated organic compounds, thereby promoting thedehalogenation reaction. Also, the water soluble reducing agentpermeates the soil, etc., and thus can be injected using a conduit, suchas a well, or an underground wall. Furthermore, the reduced state can beeasily recovered by adding the reducing agent according to the reducedstate during the purification operation.

When the water soluble reducing agent is used, it is preferred for thereduction step to include a mixing step of mixing the nutrient solutionwith an aqueous solution containing the reducing agent. By including themixing step, the water soluble reducing agent and the nutrient solutioncan be fully reacted, and the nutrient solution can be reduced.

In the introduction step, the reduced nutrient solution is preferablyintroduced into the contaminated object via a deep indentation providedin the ground surface. The deep indentation is a concept including aconduit inserted into the ground and set in place, a well, anunderground wall, or the like. If the deep indentation is a conduit orwell, the conduit or well preferably includes in at least a part thereofa strainer portion comprising many through-holes. The underground wallrefers to a deep groove, and typically refers to one formed with ahighly water permeable filler, such as sand or gravel, fitted into thegroove so that the groove will not collapse. The underground wall hasexcellent air permeability and water permeability.

In the ground with satisfactory water permeability, the reduced nutrientsolution may be introduced via a permeation gutter or a shallowindentation such as a trench. As the ground with satisfactory waterpermeability, a stratum comprising sand, gravels or pumice, for example,can be cited. The depth of the trench depends on how easily the groundcollapses. Near a place where vehicles, etc. pass, for example, thetrench may be about 20 to 30 cm deep, or even deeper. At a place wherevehicles, etc. do not pass and the ground is stable, the depth may beabout 1 m or more. The wall of the trench may be reinforced to preventcollapse, or need not be reinforced.

According to the present invention, there is also provided apurification apparatus for purifying a contaminated object containinghalogenated organic compounds, comprising reduction means by which areducing agent having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of from 300 mV to −2400 mVreduces a nutrient solution containing a nutrient source forheterotrophic anaerobic microorganisms and water, and introduction meansby which the reduced nutrient solution is introduced into thecontaminated object via an introduction portion for introducing thereduced nutrient solution into the contaminated object.

As the reducing agent and the nutrient solution, the aforementionedreducing agent and the nutrient solution can be used preferably.

The reduction means preferably includes a contact device for bringingthe nutrient solution and the reducing agent into contact with eachother, if the reducing agent is in a solid state and is insoluble orsparingly soluble in water. If the reducing agent is water soluble, onthe other hand, the reduction means preferably includes a mixing devicefor mixing the nutrient solution and an aqueous solution containing thereducing agent. In either case, the nutrient solution can be fullyreduced with the reducing agent.

The introduction portion is preferably a deep indentation formed in theground surface. The deep indentation is a concept including a conduitinserted into the ground and set in place, a well, an underground wall,or the like. In the ground with satisfactory water permeability, thereduced nutrient solution may be introduced via a permeation gutter or ashallow indentation such as a trench.

The reduction means preferably includes an underground wall filled witha water permeable filler, and the reducing agent is preferably used asat least a part of the filler.

The reducing agent may be in a particulate form, such as sand or gravel,or need not be particles. For example, a metal powder, such as an ironpowder, having a particle size comparable to that of sand or gravel maybe used as the filler. Alternatively, the filler may contain sand orgravel, and a metal powder such as an iron powder. Alternatively, thefiller may contain a filler such as sand or gravel, and a reducing agentinsoluble or sparingly soluble in water. In this case, the filler suchas sand or gravel is a main component of the underground wall whichretains air permeability and water permeability, and the reducing agentis contained in such an amount as not to impair the air permeability andwater permeability. For example, 50% by weight or less of the reducingagent is contained, or 30% by weight or less of the reducing agent maybe contained. For example, 20% by weight or less of the reducing agentmay be contained. The underground wall may have an upper portion sealedor not sealed. Alternatively, as will be mentioned later, it may be ashallow indentation, rather than a deep indentation.

The introduction means preferably has a pump.

Moreover, the purification apparatus preferably has pumping means forintroducing the contaminated object into the introduction portion forcirculation treatment of the contaminated object. In this case, thecontaminated object is mixed in the reduction means a plurality oftimes, and thereby dehalogenated more fully.

According to another aspect of the present invention, there is provideda purification method for purifying a contaminated object containinghalogenated organic compounds, including a water reduction step ofreducing water with a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of 300mV to −2400 mV, a contact step of bringing the water reduced in thereduction step into contact with a nutrient source for heterotrophicanaerobic microorganisms to obtain a mixture containing the nutrientsource, and an addition step of adding the mixture obtained in thecontact step to the contaminated object.

According to an embodiment, there is provided a purification method forpurifying a contaminated object containing halogenated organiccompounds, including a water reduction step of reducing water with areducing agent having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of from 300 mV to −2400 mV, amixing step of mixing the water reduced in the reduction step with anutrient source for heterotrophic anaerobic microorganisms, and anaddition step of adding a mixture obtained in the mixing step to thecontaminated object.

The nutrient source may be a liquid, namely, water containing a nutrientsource, or may be a solid. In the case of the solid, there can be used,for example, a solid organic material such as compost, manure, excesssludge, sludge with a high organic matter content, or organic waste.

An embodiment in which the nutrient source is a nutrient solution willbe mainly described. In the present invention, it is preferred toinclude a nutrient solution reduction step of adding water reduced inthe reduction step to a nutrient solution containing a nutrient sourcefor heterotrophic anaerobic microorganisms to reduce the nutrientsolution, and a step of adding the nutrient, solution reduced in thenutrient solution reduction step to the contaminated object. However,reduced water and a nutrient source in the form of a solid, such aspowder, a sol or a gel may be mixed or contacted with each other. As thesolid nutrient source, an organic waste such as compost, bean curdrefuse, or beer cake, or humus soil can be used as such, or any of themwhich has been compacted into a solid or semisolid form can be used.

When the nutrient source is a solid, water, or water which has alreadybeen reduced by passage through a reducing agent may be contacted withthe solid nutrient source to dissolve the nutrient source into water.For example, water may be passed through a tank holding the solidnutrient source, or a packed column packed with the solid nutrientsource.

As the reducing agent and the nutrient solution, the above-mentionedreducing agent and nutrient solution can be used preferably.

It is preferred that a well, an underground wall, a permeation gutter, atrench or an indentation is used in the water reduction step, thecontact step, or the addition step.

According to another aspect of the present invention, there is provideda purification method for purifying a contaminated object containinghalogenated organic compounds, including a circulation step ofcirculating water so as to pass through the contaminated object, and areduction step of reducing the circulating water with a reducing agenthaving a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV.

Herein, the aforementioned “contaminated object” includes soil,groundwater, sludge, sediment, compost, manured organic substances,waste, drainage (each containing a contamination source), and all othercontaminated objects contaminated with halogenated organic compounds.Particularly, this term includes soil, groundwater, sludge (eachcontaining a contamination source), and all other contaminated objectscontaminated with halogenated organic compounds.

The aforementioned “water” includes water containing a contaminationsource such as halogenated organic compounds, and water after reductionin the reduction step. Concretely, the term “water” includes not onlygroundwater, but also free water in sludge, soil, paddy field or bottommud, and water as an aqueous solution supplied to the contaminatedobject from outside a system, such as a ground surface portion.

The purification method according to this aspect of the presentinvention involves circulating water, especially groundwater, andrepeatedly performing the reduction step for the circulating water withthe use of the reducing agent, whereby water, and the contaminatedobject in contact with water, especially sludge or solid, can bepurified merely by a reducing action.

The reduction step is preferably performed in the soil. By performingthe reduction step in the soil, there is no need to pump contaminatedgroundwater above the ground, permitting purification at a low cost.Secondary contamination, which may occur as a result of pumping of thecontaminated groundwater, can also be prevented.

The circulation step preferably has a step of taking in water in thesoil, and a step of discharging water into the soil. This circulationstep can gradually purify contaminated groundwater without causing arapid change in the composition of groundwater.

The reducing agent is preferably in a solid state, and insoluble orsparingly soluble in water. The use of such reducing agent makes itpossible to reduce circulated contaminated water repeatedly, withoutinducing a marked decrease in the reducing agent. Thus, contaminatedwater can be purified in the soil at a low cost. During thiscirculation, moreover, the contaminated object is cleaned physically,and can be purified thereby.

Alternatively, the reducing agent is preferably a water soluble reducingagent. When the water soluble reducing agent is used, permeation of thereducing agent through the soil is expected.

In the purification method of the present invention, it is preferred toinclude a reducing agent addition step of adding the reducing agent.Furthermore, the reducing agent addition step is preferably performed onthe ground surface, because handling is easy on the ground surface.Alternatively, this step may be performed in the soil. For example, thereducing agent may be mixed with the filler of the underground wall, ashas been stated earlier.

It is further preferred to have a nutrient source contact step ofbringing a nutrient source for heterotrophic anaerobic microorganismsinto contact with water before being circulated.

There may be provided a nutrient source contact step of further bringinga nutrient source for heterotrophic anaerobic microorganisms intocontact with water being circulated.

It is preferred in handling that the nutrient source is added as anutrient solution containing a nutrient source. An embodiment of addingthe nutrient source as a nutrient solution will be mainly described.However, the nutrient source in the form of a solid, such as powder, asol or a gel may be added to water being circulated.

In an embodiment using the nutrient source in this manner, water,especially groundwater, is circulated, and the reducing agent and thenutrient solution are added to water being circulated. By so doing, achemical reaction by the reducing agent, and a biodegradation reactionby anaerobic microorganisms activated by the nutrient solution arerepeatedly performed. Thus, water, and the contaminated object incontact with water, especially, sludge or soil, can be efficientlypurified.

In the addition step, which of the addition of the reducing agent andthe addition of the nutrient solution may be performed first. What isimportant is that the nutrient solution is maintained in a reduced statewhen contacted with the contaminated object. By so maintaining thenutrient solution in the reduced state, the microbial activity can beenhanced, and the contaminated object can be purified with higherefficiency.

The proportion of the nutrient source for heterotrophic anaerobicmicroorganisms and water incorporated into the nutrient solution is notrestricted. The nutrient source for heterotrophic anaerobicmicroorganisms can be selected, as desired, according to the propertiesof microorganisms in the contaminated object to be purified. As theheterotrophic anaerobic microorganisms, those stated above can be used.

In the above step of taking in water present in the soil, it ispreferred that a well, an underground wall, a permeation gutter, atrench or an indentation is used.

It is also preferred that a well, an underground wall, a permeationgutter, a trench or an indentation is used in the step of dischargingwater into the soil.

The use of the water soluble reducing agent, compared with the use ofthe reducing agent in solid state, dramatically increases the efficiencyof contact with the halogenated organic compounds, thereby promoting thedehalogenation reaction. Also, the water soluble reducing agentpermeates the soil, etc., and thus can be injected using a conduit, suchas a well, an underground wall, a permeation gutter, a trench, or ashallow indentation. Furthermore, the reduced state can be easilyrecovered by adding the reducing agent according to the reduced stateduring the purification operation.

When the water soluble reducing agent is used, moreover, it is preferredto mix the nutrient solution with an aqueous solution containing thereducing agent in the addition step. By so doing, the water solublereducing agent and the nutrient solution can be fully reacted, and thenutrient solution can be maintained in a fully reduced state.

In the addition step, the reduced nutrient is preferably introduced intothe contaminated object via a deep indentation provided in the groundsurface. The deep indentation is a concept including a conduit insertedinto the ground and set in place, a well, an underground wall, or thelike. If the deep indentation is a conduit or well, the conduit or wellpreferably includes in at least a part thereof a strainer portioncomprising many through-holes. The underground wall refers to a deepgroove, and typically refers to one formed with a highly water permeablesubstance, such as sand or gravel, filled into the groove so that thegroove will not collapse. Thus, the underground wall has excellent airpermeability and water permeability. On this occasion, the reducingagent in solid state, may be used as a filler for the underground wall,as stated earlier. Alternatively, a permeation gutter, a trench, or ashallow indentation may be used during introduction of the nutrientsolution.

According to another aspect of the present invention, there is provideda purification apparatus for purifying a contaminated object containinghalogenated organic compounds, characterized by having a reducing agenthaving a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of from 300 mV to −2400 mV, a water intake portionlocated in the contaminated object or downstream from the contaminatedobject, and a water discharge portion located upstream from the waterintake portion and located in the contaminated object or upstream fromthe contaminated object, and characterized in that water is circulatedamong the water intake portion, the reducing agent, and the waterdischarge portion to purify the contaminated object. For example, waterflows through the water intake portion, the reducing agent, and thewater discharge portion in this order. From the water discharge portion,water is discharged into the soil, flows under gravity or along the flowof groundwater, and is taken in again from the water intake portion. Thewater intake portion is preferably disposed in an aquifer.

The reducing agent preferably includes a reducing agent in a solid stateand insoluble or sparingly soluble in water.

The reducing agent preferably includes a water soluble reducing agent.

The reducing agent is preferably located between the water intakeportion and the water discharge portion. This is because groundwater isfirst taken in from the water intake portion, then transported to thereducing agent by a pump or the like, and then reduced with the reducingagent, whereafter the reduced groundwater is discharged from the waterdischarge portion. The discharged water can be moved to the water intakeportion by gravity or the flow of groundwater.

The reducing agent is preferably held in a reducing agent tank. Thereducing agent tank may be provided in the soil, or may be provided onthe ground surface.

The water intake portion or the water discharge portion is preferablyprovided in a well, an underground wall, a permeation gutter, a trenchor an indentation. It is preferred to have a pump in relation tocirculation of water. For example, the pump may be disposed between thewater intake portion and the water discharge portion. Alternatively, thepump may be disposed above the water intake portion.

It is preferred to further have a nutrient source for heterotrophicanaerobic microorganisms. It is preferred that water before beingcirculated is contacted with the nutrient source. It is preferred tocirculate water among the water intake portion, the reducing agent, thenutrient source, and the water discharge portion, thereby purifying thecontaminated object. For example, water flows through the water intakeportion, the reducing agent, the nutrient source, and the waterdischarge portion in this order, or flows through the water intakeportion, the nutrient source, the reducing agent, and the waterdischarge portion in this order, is discharged from the water dischargeportion into the soil, flows by gravity or along the flow ofgroundwater, and is taken in again from the water intake portion.

It is preferred to further have a nutrient source tank holding anutrient source.

According to another aspect of the present invention, there is provideda purification apparatus for purifying contaminated soil containinghalogenated organic compounds, which includes an indentation formed inthe ground surface above or upstream from the contaminated soil, areducing agent disposed in the indentation and having a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV, and a nutrient source for heterotrophicanaerobic microorganisms which is disposed above the reducing agent.

For example, a shallow indentation, such as a trench, may be dug in theground surface, a reducing agent may be filled as a first layer into alower part of the indentation, and a nutrient source for heterotrophicanaerobic microorganisms may be filled as a second layer into an upperpart of the indentation. In this case, the indentation is provided aboveor upstream from the contaminated object containing the halogenatedorganic compounds in the soil. Groundwater or tap water may be sprinkledover the second layer. Alternatively, rainwater may be allowed to flowinto the second layer, without performing the sprinkle. As a result, thesprinkled water or the rainwater passes through the nutrient source,turning into water containing the nutrient source, and then the water isreduced with the reducing agent. The reduced water seeps into the soil,reaching the contaminated object in the soil and purifying it.

The reducing agent is preferably a solid. The nutrient source ispreferably a solid. As the solid nutrient source, it is preferred to usea solid organic material such as compost, manure, excess sludge,sediment with a high organic matter content, or organic waste.

The reducing agent and the nutrient source may be each arranged in alayer, and the layer comprising the nutrient source covers the layercomprising the reducing agent. Since the solid nutrient source coversthe reducing agent, the reducing agent can be prevented from beingconsumed by reducing oxygen in the air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a first embodiment of the presentinvention using a solid reducing agent.

FIGS. 2(a) and 2(b) are schematic views showing the internal structureof a solid reducing agent contact tank.

FIG. 3 is a schematic view showing a second embodiment of the presentinvention using a water soluble reducing agent.

FIG. 4 is a schematic view showing a third embodiment of the presentinvention applied when there is an obstacle on the ground.

FIGS. 4A and 4B are schematic views showing a method for forming ahorizontal well.

FIG. 4C is a schematic view showing another embodiment of the presentinvention using an oblique well.

FIG. 5 is a schematic view showing a fourth embodiment of the presentinvention using a purification apparatus of a circulation treatmenttype.

FIGS. 5A and 5B are partial views showing other embodiments of thepresent invention.

FIG. 6 is a schematic view showing a fifth embodiment of the presentinvention using a purification apparatus of a circulation treatmenttype.

FIG. 7 is a schematic view showing a sixth embodiment of the presentinvention using a purification apparatus of a pumping-up circulationtype.

FIG. 8 is a schematic view showing a seventh embodiment of the presentinvention in which a purification apparatus of a pumping-up circulationtype is applied when there is an obstacle on the ground.

FIG. 9 is a schematic view showing an eighth embodiment of the presentinvention in which a purification apparatus of a circulation treatmenttype is applied when there is an obstacle on the ground.

FIG. 10 is a schematic view showing a ninth embodiment of the presentinvention in which a purification apparatus of a circulation treatmenttype capable of repeated contact with a solid reducing agent is appliedwhen there is an obstacle on the ground.

FIG. 11 is a schematic view showing a tenth embodiment of the presentinvention using an underground wall.

FIGS. 12(a) to 12(c) are explanatory drawings showing the relationbetween a water level gradient and horizontal diffusion.

FIG. 13 is a schematic view showing an eleventh embodiment of thepresent invention using a solid reducing agent.

FIG. 14 is a schematic view showing the internal structure of areduction tank when a solid reducing agent is used.

FIG. 15 is a schematic view showing a twelfth embodiment of the presentinvention using a water soluble reducing agent.

FIG. 16 is a schematic view showing a thirteenth embodiment of thepresent invention.

FIG. 17 is a schematic view showing a fourteenth embodiment of thepresent invention.

FIG. 18 is a schematic view showing the fourteenth embodiment of thepresent invention using a solid reducing agent.

FIG. 19 is a sectional view showing the internal structure of anembodiment of a reduction tank when a solid reducing agent is used.

FIG. 20 is a schematic view showing a fifteenth embodiment of thepresent invention using a water soluble reducing agent.

FIG. 21 is a schematic view showing a sixteenth embodiment of thepresent invention.

FIG. 22 is a schematic view showing a seventeenth embodiment of thepresent invention.

FIG. 23 is a schematic view showing an eighteenth embodiment of thepresent invention.

FIG. 24 is a schematic view showing a nineteenth embodiment of thepresent invention.

FIG. 25 is a schematic view showing a twentieth embodiment of thepresent invention.

FIG. 26 is a schematic view showing a twenty-first embodiment of thepresent invention.

FIG. 27 is a schematic view showing a twenty-second embodiment of thepresent invention.

FIG. 28 is a schematic view showing a twenty-third embodiment of thepresent invention.

FIG. 29 is a schematic view showing a twenty-fourth embodiment of thepresent invention.

FIG. 30 is a sectional view showing the internal structure of anembodiment of a reduction tank when a solid reducing agent is used.

FIG. 31 is a schematic view showing a twenty-fifth embodiment of thepresent invention.

FIG. 32 is a schematic view showing a twenty-sixth embodiment of thepresent invention.

FIG. 33 is a schematic view showing a twenty-seventh embodiment of thepresent invention.

REFERRED EMBODIMENTS OF THE INVENTION

The present invention will now be described in further detail withreference to the accompanying drawings, but the present invention is notrestricted thereby.

FIGS. 1 and 2(a) and 2(b) are schematic views showing a state in which apurification apparatus according to an embodiment of the presentinvention is installed.

In FIG. 1, the soil has a vadose zone 1 above a groundwater table 4, andan aquifer 2 below the groundwater table 4. Below the aquifer 2, anaquitard 3 is located.

Part of the aquifer 2 is a soil 2 a contaminated with halogenatedorganic compounds, and groundwater contained in the soil 2 a is alsocontaminated with the halogenated organic compounds.

A purification apparatus A shown in FIG. 1 is equipped with reductionmeans 10 in which a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of 300mV to −2400 mV reduces a nutrient solution containing a nutrient sourcefor heterotrophic anaerobic microorganisms and water, and introductionmeans 30 for introducing the reduced nutrient solution into thecontaminated object via an introduction portion 20 for introducing thereduced nutrient solution into the contaminated object. The reducingagent is a reducing agent in a solid state (hereinafter referred to as asolid reducing agent), and an iron powder, for example, can be usedpreferably. The iron may be in the form of stainless steel, cast iron,carbon steel, or reduced iron.

As the reducing agent in solid state, there can be preferably used atleast one reducing agent selected from the group consisting of reducediron, cast iron, iron-silicon alloy, titanium alloy, zinc alloy,manganese alloy, aluminum alloy, magnesium alloy, calcium alloy,titanium-silicon alloy, titanium-aluminum alloy, zinc-aluminum alloy,manganese-magnesium alloy, aluminum-zinc-calcium alloy, aluminum-tinalloy, aluminum-silicon alloy, and calcium-silicon alloy.

As the nutrient source, a suitable nutrient source can be used accordingto the properties of microorganisms in the contaminated object to bepurified. An example of the nutrient source which can be used preferablywhen the heterotrophic anaerobic microorganisms are methane-formingbacteria is shown in each of Tables 6 and 7 below.

TABLE 6 Culture medium for methane-forming microorganisms ConstituentFormulation Tap water 800 ml Mineral 1 solution* 50 ml/l Mineral 2solution* 50 ml/l Trace mineral solution* 10 ml/l Trace vitaminsolution* 10 ml/l NaHCO₃ 5.0 g/l Yeast Extract 1.0 g/l Polypeptone 20g/l Glucose 25 g/l Sodium citrate 25 g/l Methanol 50 ml/l L-cysteinehydrochloride solution 5.0 ml/l Na₂S.9H₂O solution 5.0 ml/l pH 6.9-7.2

The mineral 1 solution refers to a solution containing 6 g of K₂HPO₄ in1 liter of distilled water.

The mineral 2 solution refers to a solution containing 6 g of KH₂PO₄, 6g of (NH₄)₂SO₄, 12 g of NaCl, 2.6 g of MgSO₄.7H₂O, and 0.16 g ofCaCl₂.2H₂O in 1 liter of distilled water.

The trace mineral solution refers to a solution containing 1.5 g ofnitrilotriacetic acid, 3.0 g of MgSO₄.7H₂O, 0.5 g of MnSO₄.2H₂O, 1.0 gof NaCl, 0.1 g of FeSO₄.7H₂O, 0.1 g of CoSO₄ or CoCl₂, 0.1 g ofCaCl₂.2H₂O, 0.1 g of ZnSO₄, 0.01 g of CuSO₄.5H₂O, 0.01 g of AlK(SO₄)₂,0.01 g of H₃BO₃, and 0.01 g of Na₂MoO₄.2H₂O in 1 liter of distilledwater. First, nitrilotriacetic acid is dissolved while being adjusted topH 6.5 with KOH, and then the other minerals are added. Finally, thesolution is adjusted to pH 7.0 with KOH.

The trace vitamin solution refers to a solution containing 2 mg ofbiotin, 2 mg of folic acid, 10 mg of pyridoxine hydrochloride, 5 mg ofthiamine hydrochloride, 5 mg of riboflavin, 5 mg of nicotinic acid, 5 mgof calcium DL-pantothenate, 0.1 mg of vitamin B₁₂, 5 mg ofp-aminobenzoic acid, and 5 mg of lipoic acid in 1 liter of distilledwater.

TABLE 7 Culture medium for methane-forming microorganisms ConstituentAmount L-cysteine hydrochloride 0.1 g/l Polypeptone 2.0 g/l Glucose 2.5g/l Sodium citrate 2.5 g/l Methanol 5.0 ml/l Sodium bicarbonate 5.0 g/lSodium sulfide nonahydrate 0.1 g/l Yeast extract 1.0 g/l Dilution waterTap water pH 6.9-7.2

An example of the nutrient source which can be used preferably when theheterotrophic anaerobic microorganisms are sulfate-reducing bacteria isshown in Table 8 below.

TABLE 8 Culture medium for sulfate-reducing microorganisms ConstituentFormulation Tap water 1000 ml K₂HPO₄ 0.5 g/l NH₄Cl 1.0 g/l Na₂SO₄ 1.0g/l CaCl₂.2H₂O 0.1 g/l MgSO₄.7H₂O 2.0 g/l Yeast Extract 1.0 g/lFeSO₄.7H₂O 0.2 g/l Trace vitamin solution* 10 ml/l Sodium lactate 25ml/l Sodium acetate 25 ml/l Sodium thioglycolate 0.1 g/l Ascorbic acid0.1 g/l pH 6.6-7.0

An example of the nutrient source which can be used preferably when theheterotrophic anaerobic microorganisms are nitrate-reducing bacteria isshown in Table 9 below.

TABLE 9 Culture medium for nitrate-reducing microorganisms ConstituentAmount Potassium nitrate 4.5 g/l Potassium acetate 8.5 g/l Sodiumbicarbonate 5.0 g/l Magnesium chloride 0.2 g/l hexahydrate Yeast extract0.1 g/l Dilution water Tap water pH 6.9-7.4

The use of organic carbon and a culture medium, which contains 20 to 50%by weight of organic carbon, preferably 20 to 30% by weight of oxideform nitrogen, as the nutrient source is preferred, because themicroorganism population involved in the aforementioned chemicalreaction and biological reaction can be changed to suppress blackeningof the soil due to iron sulfide, etc., occurrence of a methane gas, andgeneration of foul-smelling gases such as mercaptan. Furthermore, anitrogen gas is generated, so that the resulting hydrogen gas isdiluted. The oxide form nitrogen is preferably in the form of a nitrate.As the nitrate, there can be preferably used an alkali metal salt ofnitric acid, an alkaline earth metal salt of nitric acid, iron nitrate,titanium nitrate, manganese nitrate, aluminum nitrate, or magnesiumnitrate. Particularly, sodium nitrate, potassium nitrate or calciumnitrate can be used preferably. The organic carbon is preferably a watersoluble organic carbon source. Preferably usable examples of the organiccarbon source are sugars, organic acids or their derivatives, loweralcohols, molasses waste liquor, fermentation waste liquor, and mixturesof them.

The reduction means 10 is a solid reducing agent contact tank 10containing the solid reducing agent and located above the ground. Theintroduction portion 20 is a conduit 20 installed underground whichreceives a nutrient solution in a reduced form (hereinafter referred toas a reduced nutrient solution) from the solid reducing agent contacttank 10, and which introduces the reduced nutrient solution into thecontaminated object. Typically, the conduit is a well. The introductionmeans 30 is an injection pump 30 which feeds the reduced nutrientsolution into the conduit 20.

Furthermore, the purification apparatus A of the present embodiment hasa nutrient solution preparation tank 40 for preparing the nutrientsolution according to the properties of microorganisms in thecontaminated object to be purified. The nutrient solution preparationtank 40 and the solid reducing agent contact tank 10 are connected by afirst nutrient solution supply line 41. The solid reducing agent contacttank 10 and the conduit 20 are connected by a second nutrient solutionsupply line 42. In a lower part of the conduit 20, a strainer portion 21is provided for allowing the reduced nutrient solution, which has beenfed from the solid reducing agent contact tank 10 via the secondnutrient solution supply line 42, to permeate the contaminated object.The conduit 20 is installed underground so that the strainer portion 21will be located in the underground aquifer 2.

The strainer portion is many through-holes passing through the wallsurface of the conduit. The open area ratio of the strainer portion ispreferably 10 to 50%, particularly preferably 20 to 40%. The conduitfurther has a wire netting wrapped round the strainer portion, and apacker (not shown) wound round the wall surface of the conduit otherthan the strainer portion. The wire netting is designed to preventpenetration of gravel or the like into the conduit. The packer swellswhen the conduit is fixed underground. The packer is available as apacker swelling by absorbing water, and a packer swelling when a gas isinjected.

Installation of the conduit 20 is carried out by the followingprocedure: The ground is dug with a boring machine to form a deep hole.After completion of digging, the boring machine is pulled out of thehole. Then, the conduit 20, preferably, of stainless steel, which hasthe strainer portion 21 in its lower part and has an opening top portion20 a and a closed bottom portion 20 b, is inserted into the hole. Then,the packer (not shown) wound round the conduit 20 swells, typically,owing to water in the soil. Further, silica sand or the like is put intothe hole to fill up the gap around the conduit 20. Finally, cement ispoured into an area close to the ground surface, and solidified there,completing the installation of the conduit 20.

The solid reducing agent contact tank 10 may have the top portion 10 aconnected to the first nutrient solution supply line 41 as shown in FIG.2(a), or may have the bottom portion 10 b connected to the firstnutrient solution supply line 41 as shown in FIG. 2(b). The solidreducing agent contact tank 10 includes a support floor 11 provided in alower part thereof, a solid reducing agent contact portion 12 supportedby the support floor 11, a first gap portion 13 above the solid reducingagent contact portion 12, and a second gap portion 14 below the solidreducing agent contact portion 12. The solid reducing agent contactportion 12 includes a support medium such as gravel, and the solidreducing agent coating on or mixed with the support medium. The solidreducing agent is, for example, a powder measuring 500 μm or less. Thesupport floor 11 has many small holes of a size enough to allow passageof the nutrient solution, but allow no passage of the solid reducingagent. The support floor is, for example, a plate-like member composedof stainless steel. The first gap portion 13 and the second gap portion14 are of a sufficient size such that the nutrient solution fed from thefirst nutrient solution supply line 41 flows into the solid reducingagent contact portion 12 constantly at a desired speed.

When the first nutrient solution supply line 41 is connected to the topportion 10 a of the solid reducing agent contact tank 10, as shown inFIG. 2(a), the nutrient solution fed to the top portion 10 a of thesolid reducing agent contact tank 10 flows through the solid reducingagent contact portion 12 by its own weight, and is reduced thereby. Whenthe first nutrient solution supply line 41 is connected to the bottomportion 10 b of the solid reducing agent contact tank 10, as shown inFIG. 2(b), the nutrient solution needs to be forcibly sucked by a pumpor the like provided in the second nutrient solution supply lineconnected to the top portion 10 a of the solid reducing agent contacttank 10.

It is also possible to provide a three-way valve 43 in the secondnutrient solution supply line 42 and connect a backwash water flow line44 via the three-way valve 43, as shown in FIG. 2(a). In this case,cleaning water is passed through the interior of the solid reducingagent contact tank 10 from below to above via the backwash water flowline 44, whereby the solid reducing agent contact portion 12 can bebackwashed. As a result, clogging of the solid reducing agent contactportion 12 and the pores of the support floor 11 can be prevented.

The structure of the solid reducing agent contact tank 10 shown in FIG.2(a) or 2(b) can be used as the structure of a solid nutrient sourcecontact tank. Instead of filling the support medium and the solidreducing agent into the solid reducing agent contact portion 12, a solidnutrient source for heterotrophic anaerobic microorganisms may be filledalone or together with a support medium. By passing water through thesolid nutrient source contact tank, water containing the nutrient sourcefor heterotrophic anaerobic microorganisms can be obtained. Such a solidnutrient source contact tank may be used in place of the nutrientsolution preparation tank 40 of FIG. 1 or along with the nutrientsolution preparation tank 40.

Alternatively, a support medium, the solid reducing agent, and a solidnutrient source for heterotrophic anaerobic microorganisms may becharged into the solid reducing agent contact portion 12. Such a solidreducing agent contact tank may be used in place of the nutrientsolution preparation tank 40 of FIG. 1 or along with the nutrientsolution preparation tank 40. The solid nutrient source contact tank andthe solid reducing agent containing the solid nutrient source forheterotrophic anaerobic microorganisms can be similarly applied to otherembodiments of the present invention.

A purification method for a contaminated object, such as groundwater orsoil, contaminated with halogenated organic compounds, the purificationmethod using the purification apparatus A of the present embodiment,includes a reduction step in which a reducing agent having a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of from 300 mV to −2400 mV reduces a nutrient solution containing anutrient source for heterotrophic anaerobic microorganisms and water,and an introduction step in which the reduced nutrient solution isintroduced into the contaminated object after, preferably immediatelyafter, the reduction step. The reduction step is performed inside thesolid reducing agent contact tank 10, and the introduction step isperformed in the conduit 20. In detail, suitable nutrients and water areadded to the nutrient solution preparation tank 40, and thoroughlystirred to prepare a nutrient solution. The amount of water added is notrestricted, and can be set arbitrarily in such a range as to avoid thesituation that the groundwater level near the well rises to reach thesurface of the earth.

Then, the prepared nutrient solution is supplied to the solid reducingagent contact tank 10 by the injection pump 30 via the first nutrientsolution supply line 41. The nutrient solution fed to the solid reducingagent contact tank 10 contacts the solid reducing agent while passingthrough the solid reducing agent contact portion 12, and is reducedthereby. The fully reduced nutrient solution passes through the smallholes of the support floor 11 and the second gap portion 14, and is thenflowed into the conduit 20 via the second nutrient solution supply line42 while being maintained in the reduced condition. The reduced nutrientsolution flowed into the conduit 20 permeates the contaminated objectvia the strainer portion 21 formed in the lower part of the conduit 20.As a result, the reduced nutrient solution reacts with the halogenatedorganic substances contained in the contaminated object to dehalogenatethem, and simultaneously enhances the activity of the heterotrophicanaerobic microorganisms present in the contaminated object to promote abiodegradation reaction by the microorganisms, thereby purifying thecontaminated object.

Next, a second embodiment of the purification apparatus of the presentinvention is shown in FIG. 3. FIG. 3 is a schematic view showing a stateof installation of the purification apparatus using a water solublereducing agent as the reducing agent. As the water soluble reducingagent, there can be preferably used an organic acid or its derivative,hypophosphorous acid or its derivative, or a salt of an organic acid orhypophosphorous acid with iron, titanium, zinc, manganese, aluminum ormagnesium, or a sulfide salt. As the organic acid, a carboxylic acid, asulfonic acid, a phenolic acid, or a derivative thereof can be usedpreferably. Preferably used examples of the carboxylic acid aremonocarboxylic acids, dicarboxylic acids, tricarboxylic acids andtetracarboxylic acids having 1 to 20 carbon atoms and optionallysubstituted by hydroxyl groups. Concretely, acetic acid, citric acid andterephthalic acid are preferred, and aliphatic tricarboxylic acidshaving 2 to 10 carbon atoms, such as citric acid, are particularlypreferred.

As previously shown in the Table 5, formic acid and oxalic acid do nothave a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV, and do not conform to thereducing agent of the present invention. However, derivatives of formicacid and oxalic acid, for example, their salts, may have a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV, and can conform to the reducing agent of thepresent invention.

As the derivative of the phenolic acid, a polyhydroxyaryl can be usedpreferably. As the polyhydroxyaryl, 1,2,3-trihydroxybenzene and1,4-dihydroxybenzene are preferred. As the derivatives of the organicacid, salts, esters, amides, and acid anhydrides are preferred. As thederivatives of hypophosphorous acid, salts and esters can be usedpreferably, and salts are particularly preferred.

A purification apparatus B of the present embodiment is the same as inthe first embodiment shown in FIG. 1, except that the reduction means isa water soluble reducing agent mixing device 100, and a water solublereducing agent tank 150, a reducing agent supply line 151, and a pump160 provided in the reducing agent supply line 151 are included. Thesame elements as in FIG. 1 are illustrated using the same numerals. Thewater soluble reducing agent mixing device 100 accepts a first nutrientsolution supply line 141 from a nutrient solution preparation tank 140,and a reducing agent supply line 151 from the water soluble reducingagent tank 150. In the present embodiment, the water soluble reducingagent mixing device 100 is a line mixer 100. A second nutrient solutionsupply line 142 is connected between the water soluble reducing agentmixing device 100 and a conduit 20 installed underground. The conduit 20has a strainer portion 21 formed in a lower part thereof.

A purification method for a contaminated object using the purificationapparatus B of the present embodiment includes a reduction step in whicha reducing agent having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of from 300 mV to −2400 mVreduces a nutrient solution containing a nutrient source forheterotrophic anaerobic microorganisms and water, and an introductionstep in which the reduced nutrient solution is introduced into thecontaminated object after, preferably immediately after, the reductionstep. The reduction step is performed inside the water soluble reducingagent mixing device 100, and the introduction step is performed in theconduit 20. In detail, water and a culture medium suitable for theproperties of microorganisms in the contaminated object to be purifiedare added to the nutrient solution preparation tank 140, and thoroughlystirred. On the other hand, the water soluble reducing agent tank 150 ischarged with a water soluble reducing agent suitable for thecontaminated object. The resulting nutrient solution is supplied fromthe nutrient solution preparation tank 140 to the water soluble reducingagent mixing device, i.e., line mixer, 100 by the pump 130 via the firstnutrient solution supply line 141. The water soluble reducing agent issupplied from the water soluble reducing agent tank 150 to the watersoluble reducing agent mixing device, i.e., line mixer, 100 by the pumpP via the reducing agent supply line 151. In the line mixer 100, thenutrient solution and the water soluble reducing agent are thoroughlymixed, whereby the nutrient solution is reduced. The reduced nutrientsolution is flowed into the conduit 20 via the second nutrient solutionsupply line 142, and permeates the contaminated object via the strainerportion 21 formed in the lower part of the conduit 20. As a result, thereduced nutrient solution reacts with the halogenated organic compoundscontained in the contaminated object to dehalogenate them, andsimultaneously enhances the activity of the microorganisms present inthe contaminated object to promote a biodegradation reaction, therebypurifying the contaminated object.

Next, a third embodiment of the present invention is schematically shownin FIG. 4. A purification apparatus C of the present embodiment is inthe same configuration as the purification apparatus A shown in FIG. 1,except that an introduction portion 220 having a pair of inclinedportions, 220 c and 220 d, and a strainer portion 221 inserted laterallyin an aquifer 2 is provided instead of the conduit 20 of thepurification apparatus A shown in FIG. 1. The first inclined portion 220c has an open end 220 a located on the ground surface, and accepts anutrient solution, which has been reduced in a solid reducing agentcontact tank 210, from the open end 220 a via a second nutrient solutionsupply line 241. The strainer portion 221 is located horizontally in theaquifer 2, and allows the reduced nutrient solution to pass into theaquifer 2. The second inclined portion 220 d has a closed end 220 bprotruding from the ground surface. Alternatively, the water solublereducing agent mixing device 100 shown in FIG. 3 may be used in place ofthe solid reducing agent contact tank 210.

A so-called horizontal well as shown in FIG. 4 can be formed in themanner shown in FIGS. 4A and 4B. First, a hole is dug horizontally froman entrance 252 on the ground surface toward an exit 254 with the use ofa horizontal digging machine 250. When digging of the hole is completed,a reamer appears on the ground surface from the exit 254.

Then, as shown in FIG. 4B, a flexible pipe 220 c or the like is insertedinto the hole from the exit 254, and the reamer used during digging ispulled at the entrance 252. As a result, the reamer is returned to theentrance 252 through the hole to install the flexible pipe in the hole.Finally, the exit 254 may be filled up, if desired.

A purification method for the contaminated object, which uses thepurification apparatus C of the present embodiment, is the same as thefirst or second embodiment, except that the reduced nutrient solutionflows out vertically from the strainer portion 221. The purificationapparatus C and purification method of the present embodiment areeffective when there is a building, such as a plant, on the groundsurface directly above groundwater or soil including a contaminatedobject to be purified.

In FIG. 4, the strainer portion 221 extends horizontally, but thestrainer portion may be inclined. Depending on the method of formation,the inclined portion 220 d can be omitted.

A case in which the strainer portion is inclined is shown in FIG. 4C.The same elements as in FIG. 4 are assigned the same numerals, and theirexplanations are omitted. When there is a building 9 above acontaminated site 2 a, a well cannot be dug vertically from inside thebuilding. In this case, an oblique well 222 may be dug from outside thebuilding toward the contaminated site 2 a. A strainer portion 223 isprovided at the end of the oblique well 222, and the strainer portion223 preferably arrives at the contaminated site 2 a. A nutrient solutionreduced in a reduction tank 210 flows into the contaminated site 2 a viathe strainer portion 223 of the oblique well 222, and the synergisticeffect of a biological dehalogenation reaction associated with thenutrient solution and a chemical dehalogenation reaction associated withthe reducing agent purifies the contaminated site.

Next, a fourth embodiment and a fifth embodiment of the presentinvention are schematically shown in FIGS. 5 and 6. The presentembodiment is a purification apparatus D of a reduced nutrient solutioncirculation treatment type. FIG. 5 shows the use of a solid reducingagent as the reducing agent, while FIG. 6 shows the use of a watersoluble reducing agent as the reducing agent.

The purification apparatus D shown in FIG. 5 is equipped with reductionmeans 310 in which a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of from300 mV to −2400 mV reduces a nutrient solution containing a nutrientsource for heterotrophic anaerobic microorganisms and water,introduction means 330 for introducing the nutrient solution into thecontaminated object via an introduction portion 320 for introducing thereduced nutrient solution into the contaminated object, and pumpingmeans 360 for introducing the contaminated object into the introductionportion 320. As the reducing agent, the aforementioned solid reducingagent can be used. As the nutrient source, a suitable nutrient sourcecan be used according to the microbial activity in the contaminatedobject to be purified. The reduction means 310 is a solid reducing agentcontact portion 310. The introduction portion 320 is a conduit 320installed underground. The introduction means 330 is an injection pump330. The pumping means 360 is a submerged pump 360.

A top portion 320 a of the conduit 320 is preferably closed to cut offthe interior of the conduit 320 from the outside air. If desired, thepressure inside the conduit 320 can be increased.

The purification apparatus D further includes a nutrient solutionpreparation tank 340 provided on the ground, and a first nutrientsolution supply line 341 for feeding the nutrient solution prepared inthe nutrient solution preparation tank 340 to the solid reducing agentcontact portion 310. The injection pump 330 is provided in the firstnutrient solution supply line 341.

In the purification apparatus D, the solid reducing agent contactportion 310 is located in the introduction portion, i.e., the conduit320. The solid reducing agent contact portion 310 includes a supportmedium such as gravel, and a solid reducing agent attaching to thesupport medium. The conduit 320 has an upper strainer portion 321 and alower strainer portion 322, each comprising a plurality of holes formedin a wall surface. The upper strainer portion 321 and the lower strainerportion 322 are formed at spaced apart locations in the wall surface ofthe conduit 320, and the lower strainer portion 322 is located in anaquifer 2. The upper strainer portion 321 may be disposed in the aquifer2, or disposed in a vadose zone 1. When the operation of thepurification apparatus D is started, with the upper strainer portion 321being disposed in the vadose zone 1 slightly above a groundwater table4, the groundwater table 4 may locally fluctuate, whereupon the positionof the upper strainer portion 321 may be in the aquifer 2.

The solid reducing agent contact portion 310 is located between theupper strainer portion 321 and the lower strainer portion 322. Thesubmerged pump 360 is provided in the conduit 320 at a position belowthe solid reducing agent contact portion 310 and above the lowerstrainer portion 322, and extracts groundwater from the aquifer 2 intothe conduit 320. A line mixer 370 is located above the solid reducingagent contact portion 310 and below the upper strainer portion 321. Thelower strainer portion 322 functions as a through-hole for introducingthe contaminated object, especially groundwater, into the conduit 320.The upper strainer portion 321 functions as a through-hole forintroducing the nutrient solution, reduced in the solid reducing agentcontact portion 310, into the contaminated object.

The line mixer 370 mixes the groundwater, which has been pumped up bythe submerged pump 360 from the aquifer 2 via the lower strainer portion322 and reduced in the solid reducing agent contact portion 310, withthe nutrient solution injected via the nutrient supply line 341.

A purification method for groundwater, which uses the purificationapparatus D of the present embodiment, includes a reduction step inwhich a reducing agent having a standard electrode potential, relativeto a standard hydrogen electrode at 25° C., of 300 mV to −2400 mVreduces a nutrient solution containing a nutrient source forheterotrophic anaerobic microorganisms and water, and an introductionstep in which the reduced nutrient solution is introduced into thecontaminated object after, preferably immediately after, the reductionstep. The reduction step is performed inside the solid reducing agentcontact portion 310, and the introduction step is performed in theconduit 320.

In detail, water and a culture medium suitable for the properties ofmicroorganisms in groundwater are thoroughly agitated and mixed in thenutrient solution preparation tank 340 to prepare a nutrient solution.Then, the nutrient solution is supplied to the solid reducing agentcontact portion 310 in the conduit 320 via the first nutrient solutionsupply line 341. Thus, the nutrient solution is contacted with the solidreducing agent, and reduced thereby. The reduced nutrient solution ispassed through the line mixer 370, and introduced into the groundwaterin the aquifer 2 via the upper strainer portion 321.

Simultaneously, contaminated groundwater is pumped up from the aquifer 2into the conduit 320 by the submerged pump 360 via the lower strainerportion 322. The pumped up, contaminated groundwater is brought intocontact with the solid reducing agent and the reduced nutrient solutionin the solid reducing agent contact portion 310, and further sent to theline mixer 370, where the groundwater, the solid reducing agent and thereduced nutrient solution are thoroughly mixed.

Alternatively, the nutrient solution is poured over the solid reducingagent contact portion 310 via the first nutrient solution supply line341. On the other hand, the extracted, contaminated groundwater isreduced in the solid reducing agent contact portion 310. The nutrientsolution and the reduced groundwater are thoroughly mixed in the linemixer 370.

In this manner, the groundwater contaminated with halogenated organiccompounds is purified by a dehalogenation reaction by the reducing agentand a biodegradation reaction by the activated microorganisms. Thepurified groundwater is returned to the aquifer 2 via the upper strainerportion 321. The purified groundwater, discharged from the upperstrainer portion 321, moves downward by gravity, and is extracted againfrom the lower strainer portion 322.

As noted above, groundwater circulates between the aquifer 2 and theconduit 320. Thus, the contaminated site 2 a is supplied with thereducing agent and the nutrient source for heterotrophic anaerobicmicroorganisms, and dehalogenation proceeds through the combination ofthe chemical reaction by the reducing agent and the biodegradationreaction by the activated heterotrophic anaerobic microorganisms.

Alternatively, the line mixer 370 may be disposed between the pump 360and the solid reducing agent contact portion 310, as shown in FIG. 5A.That is, the lower strainer portion 322, pump 360, line mixer 370, solidreducing agent contact portion 310, and upper strainer portion 321 maybe arranged in this order from below to above inside the conduit 320. InFIG. 5A, the nutrient solution supply line 341 extends to a regionbetween the pump 360 and the line mixer 370, so that the nutrientsolution can be injected between the pump 360 and the line mixer 370.

The pump 360 extracts groundwater from the lower strainer portion 322,the nutrient solution is poured into this groundwater, and thegroundwater and the nutrient solution are mixed in the line mixer 370.The groundwater containing the nutrient solution is reduced with thereducing agent, and then discharged from the upper strainer portion 321.

Alternatively, the line mixer may be omitted, as shown in FIG. 5B. Thatis, the lower strainer portion 322, pump 360, solid reducing agentcontact portion 310, and upper strainer portion 321 may be arranged inthis order from below to above inside the conduit 320. The nutrientsolution supply line 341 may be extended to a region below the pump 360,and the nutrient solution may be injected below the pump 360. In thiscase, groundwater sucked from the lower strainer portion 322 and thenutrient solution can be mixed inside the pump 360.

Alternatively, the nutrient solution supply line 341 may be extended toa region above or below the solid reducing agent contact portion 310,and the nutrient solution may be injected above or below the solidreducing agent contact portion 310. In this embodiment, the groundwaterand the nutrient solution spontaneously mix while they are moving insidethe piping. When the nutrient solution is injected above or below thesolid reducing agent contact portion 310, especially when the nutrientsolution is injected above the pump 360, it is preferred to provide acheck valve for preventing reverse flow of the groundwater into thenutrient solution supply line 341.

When the line mixer is omitted, there may be an alternative arrangementin which the lower strainer portion 322, solid reducing agent contactportion 310, pump 360, and upper strainer portion 321 are arranged inthis order from below to above inside the conduit 320.

FIG. 6 is a schematic view showing a purification apparatus E of acirculation treatment type using a water soluble reducing agent as areducing agent. The purification apparatus E differs from thepurification apparatus D shown in FIG. 5 in that the solid reducingagent contact portion 310 of the purification apparatus D is notincluded, but a line mixer 410, a water soluble reducing agent tank 450,and a reducing agent supply line 451 are included. That is, thepurification apparatus E is equipped with reduction means 410 in which areducing agent having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of from 300 mV to −2400 mVreduces a nutrient solution containing a nutrient source forheterotrophic anaerobic microorganisms and water, introduction means 430for introducing the reduced nutrient solution into the contaminatedobject via an introduction portion 420 for introducing the reducednutrient solution into the contaminated object, and pumping means 460for introducing the contaminated object into the introduction portion420. As the water soluble reducing agent, the aforementioned watersoluble reducing agent can be used. The nutrient source may be asuitable nutrient source adapted for the microbial activity in thecontaminated object. The reduction means 410 is a line mixer 410provided on the ground surface. The introduction portion 420 is aconduit 420 installed underground. The pumping means 460 is a submergedpump 460 and a lower strainer portion 422 which are provided in theconduit 420.

The purification apparatus E further includes a nutrient solutionpreparation tank 440 provided on the ground, a first nutrient solutionsupply line 441 extending from the nutrient solution preparation tank440, an injection pump 430 provided in the first nutrient solutionsupply line 441, a water soluble reducing agent tank 450, a reducingagent supply line 451 extending from the water soluble reducing agenttank 450, and an injection pump 455 provided in the reducing agentsupply line 451. The first nutrient solution supply line 441 and thereducing agent supply line 451 are connected to the line mixer 410provided on the ground surface. Inside the conduit 420, reduction meansfor reducing the nutrient solution is not provided, unlike FIG. 5.

To purify groundwater using the purification apparatus E of the presentembodiment, the first step is to prepare water and a culture medium,suitable for the properties of microorganisms in the groundwater, in thenutrient solution preparation tank 440, and place a suitable watersoluble reducing agent in the water soluble reducing tank 450. Then, theline mixer 410 is fed with the nutrient solution from the first nutrientsolution supply line 441, and the water soluble reducing agent from thereducing agent supply line 451, and the nutrient solution and the watersoluble reducing agent are mixed in the line mixer 410. The nutrientsolution is reduced with the water soluble reducing agent in the linemixer.

The reduced nutrient solution is supplied via a pipe to a region below aline mixer 470 disposed in the conduit 420. On the other hand,groundwater is introduced into the conduit 420 by the submerged pump 460via the lower strainer portion 422. The submerged pump 460 introducesthe groundwater, which has been introduced into the conduit 420, and thereduced nutrient solution into the line mixer 470, and mixes them in theline mixer 470. A mixture of the groundwater and the reduced nutrientsolution permeates an aquifer 2 via the upper strainer portion 421, andis extracted again into the conduit 420 via the lower strainer portion422 by means of the submerged pump 460. In this manner, circulation ofthe reduced nutrient solution and the groundwater takes place. Duringthis circulation, the contaminated groundwater is subjected to adehalogenation reaction by the reducing agent and a biodegradationreaction by the activated heterotrophic anaerobic microorganisms, andpurified thereby.

FIG. 7 is a schematic view showing a sixth embodiment of the presentinvention. This embodiment is the same as the embodiment shown in FIG. 5or 6, except that a pair of wells each having a strainer portion areprovided instead of the upper strainer portion and the lower strainerportion of FIG. 5 or 6. The present embodiment shows a purificationapparatus F of a circulation treatment type. The purification apparatusF is equipped with reduction means 510, introduction means 530 forintroducing a reduced nutritive material via an introduction portion520, and pumping means 560. This embodiment uses the use of a solidreducing agent as a reducing agent. The reduction means 510 is a solidreducing agent contact tank 510. The introduction portion 520 is a pairof injection wells 520 and 520′. The nutritive material introductionmeans 530 is a submerged pump 560 located in a lower part of a pumpingwell 580.

The purification apparatus F includes a nutrient solution preparationtank 540, an injection pump 530 for feeding a nutrient solution from thenutrient solution preparation tank 540 into the injection wells via thesolid reducing agent contact tank 510, a first nutrient solution supplyline 541 connecting the nutrient solution preparation tank 540 and thesolid reducing agent contact tank 510, a second nutrient solution supplyline 542 extending from the solid reducing agent contact tank 510 andaccepted by the injection wells 520, 520′, the pumping well 580, and acontaminated object introduction line 543 for introducing a contaminatedobject, which has been extracted by the submerged pump 560 via thepumping well 580, into the nutrient solution preparation tank 540. Thestructure of the solid reducing agent contact tank 510 is the same asdescribed in FIGS. 2(a) and 2(b). The injection wells 520, 520′,respectively, have open top portions 520 a, 520 a′, closed bottomportions 520 b, 520 b′, and strainer portions 521, 521′ comprising manyopenings formed in lower parts thereof. The pumping well 580 has an opentop portion 580 c, a closed bottom portion 580 b, and a strainer portion522 comprising many openings formed in a lower part thereof, andincludes a submerged pump 560 located at the closed bottom portion 580b. The injection wells 520, 520′ and the pumping well 580 are installedunderground such that their respective strainer portions 521, 521′, 522are located in the aquifer 2, and that the pumping well 580 is locatedbetween the pair of injection wells 520.

The strainer portions 521, 521′ of the injection wells 520, 520′ may bedisposed in the vadose zone 1. The strainer portions 521, 521′ of theinjection wells 520, 520′ are preferably arranged upstream from thestrainer portion 522 of the pumping well 580. Particularly, it ispreferred that when groundwater is pumped up by the pumping means 560,the strainer portions 521, 521′ of the injection wells 520, 520′ arearranged upstream from the strainer portion 522 of the pumping well 580with respect to the flow of the groundwater.

In the purification apparatus F of the present embodiment, the reducednutrient solution introduced into the aquifer 2 via the strainerportions 521, 521′ of the pair of injection wells 520, 520′ isintroduced into the pumping well 580 from the aquifer 2 via the strainerportion 522 of the pumping well 580 located between the injection wells520 and 520′ to produce a great water level gradient, thus increasingthe speed of circulation. Moreover, the contaminated object circulatesbetween the pumping well 580 and the injection wells 520, 520′, thuspreventing spread of the contaminated object. Furthermore, the locationsof installation of the injection wells 520, 520′ and pumping well 580can be changed according to the size of the contaminated site.

The present embodiment shows the use of the solid reducing agent. When awater soluble reducing agent is used, a water soluble reducing agentmixing portion 510′ may be used in place of the solid reducing agentcontact tank 510.

FIG. 8 is a schematic view showing an application example in which apurification apparatus G of a circulation treatment type similar to thatin the sixth embodiment shown in FIG. 7 is applied when there is anobstacle, such as a plant, on the soil containing a contaminated objectto be purified. The purification apparatus G is equipped with reductionmeans 610, introduction means 630 for introducing a reduced nutrientsolution into the contaminated object via an introduction portion 620,and pumping means 660. The reduction means 610 is a solid reducing agentcontact tank or water soluble reducing agent mixing tank 610. Theintroduction means 620 is an injection well 620 including an open topportion 620 a, a closed bottom portion 620 b, and a strainer portion 621comprising many openings formed in a lower part thereof. Theintroduction means 630 is an injection pump 630. The pumping means 660is a submerged pump 660. The injection pump 630 is provided in a firstnutrient solution supply line 641 for supplying a nutrient solution froma nutrient solution preparation tank 640. The first nutrient solutionsupply line 641 is connected to the solid reducing agent contact tank orwater soluble reducing agent mixing tank 610. The solid reducing agentcontact tank or water soluble reducing agent mixing tank 610 isconnected to a second nutrient solution supply line 642, and the secondnutrient solution supply line 642 is accepted into the injection well620. A pumping well 680 has an open top portion 680 a, a closed bottomportion 680 b, and a strainer portion 622 comprising many openingsformed in a lower part thereof, and includes a submerged pump 660located at the closed bottom portion 680 b. The pumping well 680 and thenutrient solution preparation tank 640 are connected by a contaminatedobject supply line 643.

The injection well 620 and the pumping well 680 are installed such thatin an aquifer 2, the injection well 620 is located upstream in the flowof groundwater, while the pumping well 680 is located downstream in theflow of groundwater. The distance between the injection well 620 and thepumping well 680 is appropriately selected depending on the size of theobstacle present on the ground.

To purify groundwater by use of the purification apparatus G of thepresent embodiment, the nutrient solution is supplied from the nutrientsolution preparation tank 640 to the solid reducing agent contact tank610 via the first nutrient solution supply line 641. After reduction ofthe nutrient solution, the reduced nutrient solution is introduced intothe injection well 620 via the second nutrient solution supply line 642,and then introduced into the contaminated object in the aquifer 2through the strainer portion 621 located in the lower part. In theaquifer 2, groundwater flows from the injection well 620 toward thepumping well 680. Thus, the contaminated object and the purified objectare introduced into the pumping well 680 by the submerged pump 660, andthen introduced into the nutrient solution preparation tank 640 via thecontaminated object supply line 643. In this manner, it becomes possibleto purify the contaminated object into which the reduced nutrientsolution cannot be directly introduced because of the presence of theobstacle. When the injection well 620 is installed at a relativelyshallow position, and the pumping well 680 is installed at a relativelydeep position, the following advantage is produced: The reduced nutrientsolution flowing out of the injection well 620 flows into the pumpingwell 680 under its own weight. This flow, coupled with the flow ofgroundwater, increases the circulation speed of the reduced nutrientsolution. The present embodiment is effective when used in a place wherethe thickness of the aquifer 2 is large.

FIG. 9 is a schematic view showing an eighth embodiment of the presentinvention. FIG. 9 shows an example of application in a place where anobstacle, such as a plant, is present on the ground and the thickness ofan aquifer 2 is not very large. A purification apparatus H of thepresent embodiment is equipped with reduction means 710, andintroduction means 730 for introducing a reduced nutrient solution viaan introduction portion 720. The reduction means 710 is a solid reducingagent contact tank or a water soluble reducing agent mixing tank. Theintroduction portion 720 has an open end portion 720 a, a first inclinedportion 720 c extending obliquely from the open end portion 720 a intothe ground, a horizontal portion 720 e connected to the first inclinedportion 720 c and inserted horizontally in the aquifer 2, a secondinclined portion 720 d connected to the horizontal portion 720 e andextending obliquely toward an above-ground region, and a closed endportion 720 b which is an above-ground end portion of the secondinclined portion 720 d. The open end portion 720 a accepts a secondnutrient solution supply line 742 extending from the solid reducingagent contact tank 710. The first inclined portion 720 c is locateddownstream in the flow of groundwater in the aquifer 2. The secondinclined portion 720 d is located upstream in the flow of groundwater inthe aquifer 2. The closed end portion 720 b is closed above the groundin a protruding state. The horizontal portion 720 e includes adownstream strainer portion 721 a, a submerged pump 760, a line mixer770, and an upstream strainer portion 721 b in this order. The submergedpump 760 sucks contaminated groundwater from the aquifer 2 into thehorizontal portion 720 e via the downstream strainer portion 721 a, andsupplies it to the line mixer 770. The sucked contaminated groundwateris mixed with the reduced nutrient solution, which has been suppliedfrom the second nutrient solution supply line 742, in the line mixer770, and is purified thereby. The reduced nutrient solution and purifiedgroundwater mixed in the line mixer 770 are returned into the aquifer 2via the upstream strainer portion 721 b. The introduction means 730 isan injection pump 730 provided in a first nutrient solution supply line741 from a nutrient solution preparation tank 740.

The purification apparatus H of the present embodiment has the followingadvantages: It is effective when an obstacle, such as a plant, ispresent on the ground and the thickness of groundwater in the aquifer 2is small. This apparatus can circulate contaminated groundwater withoutpumping it, thus obviating the need for pumping treatment.

In FIG. 9, the horizontal portion 720 e extends in a horizontaldirection, but the horizontal portion may be inclined. Depending on themethod of formation, the inclined portion 720 d may be omitted.

As shown in FIG. 9, the horizontal portion 720 e may be located below acontaminated soil 2 a, or the horizontal portion 720 e may pass throughthe center of the contaminated soil 2 a in the horizontal direction.Preferably, the horizontal portion 720 e passes through the center ofthe contaminated soil 2 a in the horizontal direction. Particularly, theupstream strainer portion 721 b and the downstream strainer portion 721a are preferably located upstream and downstream from the contaminatedsoil 2 a with respect to a flow 790 of groundwater. More preferably,they are located slightly upstream and downstream from the contaminatedsoil 2 a.

FIG. 10 shows a ninth embodiment of the present invention. Apurification apparatus I of the ninth embodiment is in the sameconfiguration as the eighth embodiment shown in FIG. 9, except that thereduction means, i.e., solid reducing agent contact portion 810, islocated not above the ground, but in a horizontal portion 820 e locatedhorizontally in the aquifer 2. That is, the horizontal portion 820 eincludes a downstream strainer portion 821 a, a submerged pump 860, aline mixer 870, and an upstream strainer portion 721 b in this order.

The submerged pump 860 sucks contaminated groundwater from the aquifer 2into the horizontal portion 820 e via the downstream strainer portion821 a, and supplies it to the line mixer 870. The sucked contaminatedgroundwater is mixed with a nutrient solution, which has been suppliedfrom a second nutrient solution supply line 841, in the line mixer 870.The nutrient solution and groundwater mixed in the line mixer 870 arereduced in the solid reducing agent contact portion 810, and thenreturned into the aquifer 2 via the upstream strainer portion 821 b.

In this case, there are the advantage obtained in the eighth embodiment,and also the advantage that a dehalogenation reaction can be performedmore sufficiently, since groundwater contacts the reducing agentrepeatedly.

As shown in FIG. 10, the horizontal portion 820 e may be located below acontaminated soil 2 a, or the horizontal portion 820 e may pass throughthe center of the contaminated soil 2 a in the horizontal direction.Preferably, the horizontal portion 820 e passes through the center ofthe contaminated soil 2 a in the horizontal direction. Particularly, theupstream strainer portion 821 b and the downstream strainer portion 821a are preferably located upstream and downstream from the contaminatedsoil 2 a with respect to a flow 890 of groundwater. More preferably,they are located slightly upstream and downstream from the contaminatedsoil 2 a.

FIG. 11 shows a tenth embodiment of the present invention. Apurification apparatus J of the present embodiment is in the sameconfiguration as the seventh embodiment shown in FIG. 8, except that apair of underground walls comprising an injection wall 920 and a pumpingwall 980 are utilized instead of the injection well 620 and the pumpingwell 680 of the purification apparatus G. Since the underground walls920 and 980 are the same in structure, the underground wall 920 will betaken as an example to illustrate the structure of the underground wall.The underground wall 920 comprises an open end portion 920 a, a deepgroove 920 c dug in the ground, and a bottom portion 920 b. In the deepgroove 920 c, an element with high permeability to air and liquid, suchas sand or gravel, is buried to prevent collapse of the groove. The deepgroove 920 c of the underground wall 920 forms a side wall of theunderground wall, and is formed with a deposition of the element havingexcellent air and liquid permeability. Thus, the entire wall surfaceexhibits the same function as that of a strainer portion. Hence, whenthe underground wall 920 is used as an introduction portion, a nutrientsolution is introduced into an aquifer 2 from any part thereof. On theother hand, the underground wall 980 includes at a bottom portion 980 ba submerged pump 960 for extracting groundwater from the aquifer 2.Groundwater is introduced into the pumping wall 980 from theneighborhood of the bottom portion 980 b. When the underground walls 920and 980 are used, the reduced nutrient solution is introduced into theaquifer 2 from any part of the injection wall 920, and groundwater isextracted by the submerged pump 960 from the lower part of the pumpingwall 980. These features lead to the advantages that the reducednutrient solution can be diffused over a broad range in the horizontaldirection, when the water level of groundwater of the aquifer 2 is highand its water level gradient is small.

FIGS. 12(a), 12(b) and 12(c) show water level contour lines as solidlines, and groundwater stream lines as arrows. FIGS. 12(a) and 12(b)show water level contour lines and groundwater stream lines when wellshaving strainer portions are used. When the water level gradient isgreat, the nutrient solution can diffuse widely in the horizontaldirection, as shown in FIG. 12(a). When the water level gradient issmall, the horizontal diffusion of the nutrient solution is limited, asshown in FIG. 12(b). This is because the amount of outflow from thestrainer portion is too small to obtain a horizontal diffusive effectsurpassing the water level gradient.

However, even when the water level gradient is small, the use of theunderground wall enables the nutrient solution to diffuse horizontallyover a wide range. FIG. 12(c) shows water level contour lines andgroundwater stream lines when underground walls are used. With theunderground wall, outflow of the nutrient solution occurs from theentire underground wall, thus permitting horizontal diffusion over abroad range.

According to an aspect of the purification apparatus and thepurification method of the present invention, a contaminated objectcontaining halogenated organic compounds can be purified efficiently andeasily. Particularly, a satisfactory biodegradation reaction due to theenhancement of the activity of heterotrophic microorganisms by a reducednutrient solution, and a dehalogenation reaction by a reducing agent arecombined together, whereby the contaminated object containing thehalogenated organic compounds can be purified satisfactorily.

According to the purification apparatus and the purification method asan aspect of the present invention, a contaminated object containinghalogenated organic compounds can be purified in situ easily andcontinuously.

FIGS. 13 and 14 are schematic views showing a state in which apurification apparatus according to an embodiment of the presentinvention is installed.

In FIG. 13, the soil has a vadose zone 1 above a groundwater table 4,and an aquifer 2 below the groundwater table 4. Below the aquifer 2, anaquitard 3 is located. Part of the aquifer 2 is a soil 2 a contaminatedwith halogenated organic compounds, and groundwater contained in thesoil 2 a is similarly contaminated with the halogenated organiccompounds.

A purification apparatus K shown in FIG. 13 is equipped with a reductiontank 1010 holding a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of from300 mV to −2400 mV, and a housing 1020 which has a water intake portion1022 and a water discharge portion 1021, and in which at least the waterintake portion 1022 is located at a site filled with flowable water inthe contaminated object, namely, located in the aquifer 2 in the presentembodiment. The purification apparatus K is configured such thatgroundwater circulates between the aquifer 2 and the housing 1020. Thereducing agent is a reducing agent in a solid state (hereinafterreferred to as a solid reducing agent), and an iron powder, for example,can be used preferably. The iron may be in the form of stainless steel,cast iron, carbon steel, or reduced iron.

As the reducing agent, there can be preferably used at least onereducing agent selected from the group consisting of reduced iron, castiron, iron-silicon alloy, titanium alloy, zinc alloy, manganese alloy,aluminum alloy, magnesium alloy, calcium alloy, titanium-silicon alloy,titanium-aluminum alloy, zinc-aluminum alloy, manganese-magnesium alloy,aluminum-zinc-calcium alloy, aluminum-tin alloy, aluminum-silicon alloy,and calcium-silicon alloy.

The water intake portion 1022 is a strainer portion comprising manythrough-holes provided in a wall surface of a lower part of the housing1020. The water discharge portion 1021 is a strainer portion comprisingmany through-holes provided in the wall surface of a nearly middle partof the housing 1020. The location of the water discharge portion 1021 isnot restricted to the middle part of the housing 1020. The housing 1020may be formed such that when the water intake portion 1022 is located inthe aquifer 2, the water discharge portion 1021 will be located in anupper part of the aquifer 2 or slightly above the aquifer 2. The openarea ratio of the strainer portion is preferably 10 to 50%, particularlypreferably 20 to 40%.

The housing 1020 further has wire nettings wrapped round the strainerportions, and a packer (not shown) wound round the wall surface of theconduit other than the strainer portions. The wire netting is designedto prevent penetration of gravel or the like into the housing 1020. Thepacker absorbs water and swells when the housing 1020 is fixedunderground. To install the housing 1020 vertically in the soil, thefollowing procedure is performed: The soil is dug with a boring machineto form a deep hole. After completion of digging, the boring machine ispulled out of the hole. Then, the housing 1020 is inserted into thehole. Then, the packer (not shown) wound round the outer peripheral wallof the housing 1020 swells by absorbing moisture present between thehousing 1020 and the soil wall. Further, silica sand or the like is putinto the hole to fill up the gap around the housing 1020. Finally,cement is poured into an area close to the ground surface, andsolidified there, completing the installation of the housing 1020.

The reduction tank 1010, as shown in FIG. 14, includes a support floor1011 provided in a lower part thereof, a solid reducing agent contactportion 1012 supported by the support floor 1011, a first gap portion1013 above the solid reducing agent contact portion 1012, and a secondgap portion 1014 below the solid reducing agent contact portion 1012.The solid reducing agent contact portion 1012 includes a support mediumsuch as gravel, and the solid reducing agent carried on the supportmedium. The solid reducing agent is, for example, a powder measuring 500μm or less. The support floor 1011 has many small holes of a size enoughto allow passage of groundwater, but allow no passage of the solidreducing agent. The support floor is, for example, a plate-like membercomposed of stainless steel. The first gap portion 1013 and the secondgap portion 1014 are of a sufficient size for groundwater to flow intothe solid reducing agent contact portion 1012 constantly at a desiredspeed.

The purification method for purifying groundwater and soil contaminatedwith halogenated organic compounds, by use of the purification apparatusK of the present embodiment, includes a circulation step of circulatinggroundwater, and a reduction step of reducing the circulatinggroundwater with a reducing agent having a standard electrode potential,relative to a standard hydrogen electrode at 25° C., of 300 mV to −2400mV.

In the circulation step, groundwater in the aquifer 2 is taken up intothe housing 1020 by a pump P via the water intake portion 1022 in thelower part of the housing 1020, and discharged into the aquifer 2 viathe water discharge portion 1021 in the middle part of the housing 1020.Then, the groundwater moves in the aquifer 2 from its upper region toits lower region by gravity.

In the reduction step, groundwater taken into the housing 1020 iscontacted with the reducing agent during its passage through thereduction tank 1010, and reduced thereby. In detail, the groundwaterflows from below the reduction tank 1010 into the reduction tank 1010,passes through the second gap portion 1014 and the small holes of thesupport floor 1011, and reaches the reducing agent contact portion 1012,where the groundwater is reduced. The groundwater reduced in thereducing agent contact portion 1012 passes through the first gap portion1013, is then returned to the interior of the housing 1020, and flowsout of the water discharge portion 1021 into the aquifer 2. In thismanner, the reduced groundwater cleans the soil.

Next, a twelfth embodiment of the purification apparatus of the presentinvention is shown in FIG. 15. FIG. 15 is a schematic view showing astate of installation of the purification apparatus using a watersoluble reducing agent as the reducing agent. As the water solublereducing agent, there can be preferably used an organic acid or itsderivative, hypophosphorous acid or its derivative, or a salt of anorganic acid or hypophosphorous acid with iron, titanium, zinc,manganese, aluminum or magnesium, or a sulfide salt. As the organicacid, a carboxylic acid, a sulfonic acid, a phenolic acid, or aderivative thereof can be used preferably. Preferably used examples ofthe carboxylic acid are monocarboxylic acids, dicarboxylic acids,tricarboxylic acids and tetracarboxylic acids having 1 to 20 carbonatoms and optionally substituted by hydroxyl groups. Concretely, aceticacid, citric acid and terephthalic acid are preferred, and aliphatictricarboxylic acids having 2 to 10 carbon atoms, such as citric acid,are particularly preferred.

As shown in the Table 1 offered earlier, formic acid and oxalic acid donot have a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV, and do not conform to thereducing agent of the present invention. However, derivatives of formicacid and oxalic acid, for example, their salts, may have a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV, and can conform to the reducing agent of thepresent invention.

As the derivative of the phenolic acid, a polyhydroxyaryl can be usedpreferably. As the polyhydroxyaryl, 1,2,3-trihydroxybenzene and1,4-dihydroxybenzene are preferred. As the derivatives of the organicacid, salts, esters, amides, and acid anhydrides are preferred. As thederivatives of hypophosphorous acid, salts and esters can be usedpreferably, and salts are particularly preferred.

A purification apparatus L of the present embodiment is the same as inthe embodiment shown in FIG. 13, except that a water soluble reducingagent is used as the reducing agent, and reducing agent addition means1030 provided on the ground surface is further provided. The sameelements as in FIG. 13 are illustrated using the same numerals.

The reducing agent addition means 1030 includes a water soluble reducingagent tank 1031, a reducing agent supply line 1032 extending from thewater soluble reducing agent tank 1031 to a reduction tank 1010 inside ahousing 1021, and a pump P3 provided on the reducing agent supply line1032. If desired, a line mixer (not shown) may be provided in thereducing agent supply line 1032.

A purification method for soil water using the purification apparatus Lof the present embodiment is the same as the purification method forsoil water using the purification apparatus K, except for initiallyproviding the step of adding a water soluble reducing agent from thewater soluble reducing agent tank 1031 into the reduction tank 1010 bythe pump P3 via the reducing agent supply line 1032.

To purify groundwater and soil using the purification apparatus L of thepresent embodiment, the water soluble reducing agent is supplied fromthe reducing agent supply line 1032 to a region below a line mixer 1070,which is disposed inside the housing 1020, via a pipe 1029. Separately,groundwater is introduced into the housing 1020 by a submerged pump 1060via a lower strainer portion 1022. The submerged pump 1060 introducesthe groundwater and water soluble reducing agent, which have beenintroduced into the housing 1020, into the line mixer 1070. In the linemixer 1070, the groundwater and water soluble reducing agent are mixedto reduce the groundwater. The reduced groundwater permeates the aquifer2 via the upper strainer portion 1021, and cleans the soil. Then, thegroundwater is extracted again into the housing 1020 by the submergedpump 1060 via the lower strainer portion 1022. In this manner,circulation of groundwater takes place. During this circulation,contaminated groundwater is degraded by the reducing agent and purifiedthereby. This groundwater is given a reducing power.

Next, a thirteenth embodiment of the present invention is schematicallyshown in FIG. 16. A purification apparatus M of the present embodimentis effective when there is an obstacle, such as a plant, abovecontaminated soil or groundwater to be purified. The purificationapparatus M is the same as the embodiment shown in FIG. 13, except thata housing 1120 a is located horizontally in an aquifer 2. The sameelements are assigned the same numerals for illustration.

Herein, the well includes a so-called horizontal well as indicated asthe housing 1120 a, and the oblique well 222 of FIG. 4C.

In the housing 1120 a, a strainer portion 1122 constituting a waterintake portion is formed downstream with respect to groundwater, and astrainer portion 1121 constituting a water discharge portion is formedupstream with respect to groundwater. The housing 1120 a includes a pumpP at a site close to the water intake potion 1122, and a reduction tank1110 at a site close to the water discharge potion 1121. If desired,communication pipes 1120 b and 1120 c communicating with the groundsurface may be provided at opposite end portions of the housing 1120 a.

That is, the strainer portion 1122 for sucking in groundwater, pump1160, reduction tank 1110 for reducing groundwater, line mixer 1170, andstrainer portion 1121 for discharging the reduced groundwater areprovided in this order inside the housing 1120 a. If groundwater cansufficiently contact the reducing agent inside the reduction tank 1110,the line mixer 1170 can be omitted.

Purification of groundwater and soil by the purification apparatus M ofthe present embodiment is performed by repeating the step of suckinggroundwater via the water intake portion 1122, passing it through thereduction tank 1110, and returning it from the water discharge portion1121 into the aquifer 2 by the action of the pump P, therebyrepetitively reacting the groundwater with the reducing agent inside thereduction tank 1110 during its circulation in the purification apparatusM to cause its reduction, and allowing the reduced groundwater to cleanthe soil repeatedly.

When the water intake portion 1122 is installed at a relativelylow-water level site, and the water discharge portion 1121 is installedat a relatively high water level site, the following advantage isproduced: The ions of the reducing agent contained in the groundwaterflowing out of the water discharge portion 1121 have their own weight,which, coupled with the flow of groundwater, increases the circulationspeed. Also, the present embodiment is effective when used in a placewhere the aquifer 2 is thick.

Further, a fourteenth embodiment of the present invention isschematically shown in FIG. 17. A purification apparatus N of thepresent embodiment is equipped with a pumping well 1280 having astrainer portion 1222 constituting a water intake portion and asubmerged pump P, a groundwater supply line 1243 for guiding groundwatersucked from the water intake portion, a reduction tank 1210 connected tothe groundwater supply line 1243 and provided on the ground surface, areducing agent supply line 1242 for guiding groundwater containing areducing agent from the reduction tank 1210, and a pair of injectionwells 1220 and 1220′ for accepting the reducing agent from the reducingagent supply line 1242 and having water discharge portions, i.e.,strainer portions 1221 and 1221′. The pair of injection wells 1220 and1220′ having the water discharge portions are located in a relativelyhigh water level region of an aquifer 2, while the pumping well 1280having the water intake portion is located in a relatively low waterlevel region of the aquifer 2.

Groundwater sucked via the water intake portion 1222 of the pumping well1280 is pumped up by the pump P to the reduction tank 1210 provided onthe ground surface via the groundwater supply line 1243. The pumped-upgroundwater contacts the reducing agent in the reduction tank 1210 toundergo a reducing action, and is then returned into the aquifer 2through the water discharge portions 1221 and 1221′ of the injectionwells 1220 and 1220′ via the reducing agent supply line 1242. Byrepeating this process, contaminated groundwater is gradually reducedand purified while circulating among the water intake portion 1222, thereduction tank 1210 and the water discharge portions 1221 and 1221′.

In a place where the layer thickness of the aquifer and the layerthickness of the vadose zone are relatively large, the fourteenthembodiment can produce a particularly great water level gradient. Thus,the speed of circulation increases, and the purification efficiencyincreases. Moreover, the contaminated groundwater circulates between thepumping well 1280 and the injection wells 1220, 1220′, thus preventingspread of the contaminated object. Furthermore, the locations ofinstallation of the injection wells 1220, 1220′ and pumping well 1280can be changed according to the size of the contaminated site.

The present embodiment shows the use of the solid reducing agent. When awater soluble reducing agent is used, a water soluble reducing agenttank, a water soluble reducing agent supply line, and a line mixer asshown in FIG. 15 may be used instead of the reduction tank 1210.

In the embodiment shown in FIG. 17, the pair of injection wells areused, but there may be one, two or more, for example, three or more ofthe injection wells. Alternatively, an underground wall may be used inplace of the injection well. The underground wall refers to somethinglike a well extending laterally to form a wall underground. Theunderground wall comprises an open end portion, a deep groove dug in theground, and a bottom portion. In the deep groove, an element with highpermeability to air and liquid, typically such as sand or gravel, isburied to prevent collapse of the groove. The deep groove of theunderground wall forms a side wall of the underground wall, and isformed with a deposition of the element having excellent air and liquidpermeability. Thus, the entire wall surface exhibits the same functionas that of a strainer portion.

In the foregoing embodiment, an example of circulating groundwater topurify groundwater and soil has been explained. However, the object tobe circulated is not limited to groundwater, and the object to bepurified is not restricted to groundwater and soil.

According to a purification apparatus and a purification method as otheraspects of the present invention, a contaminated object containinghalogenated organic compounds can be purified efficiently and easily.Particularly, water is reduced while being circulated between a sitefilled with flowable water in the contaminated object and thepurification apparatus (in the above-described embodiment, groundwateris circulated between the aquifer 2 and the purification apparatus 1).By this measure, dehalogenated water can be returned into thecontaminated object, without a rapid change in the quality of water,whereby the halogen ion concentration in the contaminated object can bedecreased gradually, and the contaminated object containing halogenatedorganic compounds can be purified satisfactorily.

According to a purification apparatus and a purification method as otheraspects of the present invention, a contaminated object containinghalogenated organic compounds can be purified easily and continuously insitu.

The present invention will be described in further detail with referenceto the accompanying drawings, but the present invention is notrestricted thereby.

FIG. 18 is a schematic view showing a state in which a purificationapparatus according to an embodiment of the present invention isinstalled. FIG. 19 is a sectional view of an embodiment of connectionbetween a water supply line and a reducing agent tank in the embodimentof FIG. 18.

In FIG. 18, the soil has a vadose zone 1 above a groundwater table 4,and an aquifer 2 below the groundwater table 4. Below the aquifer 2, anaquitard 3 is located. Part of the aquifer 2 is a soil 2 a contaminatedwith halogenated organic compounds, and groundwater contained in thesoil 2 a is similarly contaminated with the halogenated organiccompounds.

A purification apparatus 1300 shown in FIG. 18 is equipped with areducing agent tank 1310 holding a reducing agent having a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV, a nutrient solution tank 1340 containing anutrient source for heterotrophic anaerobic microorganisms, and apurification tank 1320 which has a water intake portion 1322 and a waterdischarge portion 1321, and in which at least the water intake portion1322 is located at a site filled with flowable water in the contaminatedobject, namely, located in the aquifer 2 in the present embodiment. Thepurification apparatus 1300 is configured such that groundwatercirculates between the aquifer 2 and the purification tank 1320. As thenutrient source, there can be used a nutrient source suitable for theproperties of microorganisms present in the contaminated object to bepurified.

The water intake portion 1322 is a strainer portion comprising manythrough-holes provided in a wall surface of a lower part of thepurification tank 1320. The water discharge portion 1321 is a strainerportion comprising many through-holes provided in the wall surface of anearly middle part of the purification tank 1320. The location of thewater discharge portion 1321 is not restricted to the middle part of thepurification tank 1320. The purification tank 1320 may be formed andinstalled such that when the water intake portion 1322 is located in theaquifer 2, the water discharge portion 1321 will be located in an upperregion of the aquifer 2 or slightly above the aquifer 2. The open arearatio of the strainer portion is preferably 10 to 50%, particularlypreferably 20 to 40%.

A lifting pump 1360 is installed above the water intake portion 1322 ofthe purification tank 1320 to suck groundwater from the aquifer 2 intothe purification tank 1320 via the water intake portion 1322, and pumpup the groundwater along the longitudinal direction of the purificationtank 1320.

The reducing agent tank 1310 is provided above the lifting pump 1360.The reducing agent tank 1310, as shown in FIG. 19, includes a supportfloor 1311 provided in a lower part thereof, a solid reducing agentcontact portion 1312 supported by the support floor 1311, a first gapportion 1313 above the solid reducing agent contact portion 1312, and asecond gap portion 1314 below the solid reducing agent contact portion1312. The solid reducing agent contact portion 1312 includes a supportmedium such as gravel, and a solid reducing agent carried on the supportmedium. The solid reducing agent is, for example, a powder measuring 500μm or less. The support floor 1311 has many small holes of a size enoughto allow passage of groundwater, but allow no passage of the solidreducing agent. The support floor is, for example, a plate-like membercomposed of stainless steel. The first gap portion 1313 and the secondgap portion 1314 are of a sufficient size for groundwater to flow intothe solid reducing agent contact portion 1312 constantly at a desiredspeed.

A line mixer 1370 is provided above the reducing agent tank 1310. Theline mixer 1370 is provided for mixing groundwater, which has beenreduced by passage through the reducing agent tank 1310, with thenutrient solution supplied from the nutrient solution tank 1340. As theline mixer 1370, a line mixer in customary use can be used without anyrestriction.

The nutrient solution tank 1340 is provided outwardly of thepurification tank 1320 and on the ground surface, as shown in FIG. 18.The nutrient solution tank 1340 is provided with ordinary agitationmeans to agitate and prepare the aforementioned nutrient source, asdesired. A nutrient solution supply line E1 for introducing the preparednutrient solution into the purification tank 1320 is connected to thenutrient solution tank 1340. A pump 1330 for introducing the nutrientsolution from the nutrient solution tank 1340 to the purification tank1320 is provided on the nutrient solution supply line E1.

The purification tank 1320 is a well installed underground in theembodiment shown in FIG. 18. The purification tank 1320 has wirenettings wrapped round the strainer portions, and a packer (not shown)wound round the all surface of the conduit other than the strainerportions. The wire nettings are designed to prevent penetration ofgravel or the like into the purification tank 1320. The packer absorbswater and swells when the purification tank 1320 is fixed underground.To install the purification tank 1320, i.e. well, vertically in thesoil, the following procedure is performed: The soil is dug with aboring machine to form a deep hole. After completion of digging, theboring machine is pulled out of the hole. Then, the purification tank1320 is inserted into the hole. Then, the packer (not shown) wound roundthe outer peripheral wall of the purification tank 1320 swells byabsorbing moisture present between the purification tank 1320 and thesoil wall. Further, silica sand or the like is put into the hole to fillup the gap around the purification tank 1320. Finally, cement is pouredinto an area close to the ground surface, and solidified there,completing the installation of the purification tank 1320.

The purification method for purifying groundwater and soil contaminatedwith halogenated organic compounds, by use of the purification apparatus1300 of the present embodiment, includes a circulation step ofcirculating groundwater, and a step of adding a reducing agent and anutrient solution for heterotrophic anaerobic microorganisms, thereducing agent being adapted to reduce the circulating groundwater andhaving a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV.

In the circulation step, groundwater in the aquifer 2 is taken up intothe purification tank 1320 by the lifting pump 1360 via the water intakeportion 1322 in the lower part of the purification tank 1320, anddischarged into the aquifer 2 via the water discharge portion 1321 inthe middle part of the purification tank 1320. Then, the groundwatermoves in the aquifer 2 from its upper region to its lower region bygravity.

Then, groundwater taken into the purification tank 1320 passes throughthe reducing agent tank 1310, when the reducing agent and the nutrientsolution are added to the groundwater. In detail, the groundwater flowsfrom below the reducing agent tank 1310 into the reducing agent tank1310, passes through the second gap portion 1314 and the small holes ofthe support floor 1311, and reaches the reducing agent contact portion1312, where the reducing agent is added to reduce the groundwater. Thegroundwater reduced in the reducing agent contact portion 1312 passesthrough the first gap portion 1313, and is then returned to the interiorof the purification tank 1320. Then, in the line mixer 1370, thenutrient solution introduced from the nutrient solution supply line E1to the interior of the purification tank 1320 is added to the reducedgroundwater. The groundwater thus incorporating the reducing agent andthe nutrient solution flows out of the water discharge portion 1321 intothe aquifer 2 to clean the soil. The line mixer 1370 is not an essentialelement, and can be omitted.

Next, a fifteenth embodiment of the purification apparatus of thepresent invention is shown in FIG. 20. FIG. 20 is a schematic viewshowing a state of installation of the purification apparatus using awater soluble reducing agent as the reducing agent.

As the water soluble reducing agent, there can be preferably used anorganic acid or its derivative, hypophosphorous acid or its derivative,or a salt of an organic acid or hypophosphorous acid with iron,titanium, zinc, manganese, aluminum or magnesium, or a sulfide salt. Asthe organic acid, a carboxylic acid, a sulfonic acid, a phenolic acid,or a derivative thereof can be used preferably. Preferably used examplesof the carboxylic acid are monocarboxylic acids, dicarboxylic acids,tricarboxylic acids and tetracarboxylic acids having 1 to 20 carbonatoms and optionally substituted by hydroxyl groups. Concretely, aceticacid, citric acid and terephthalic acid are preferred, and aliphatictricarboxylic acids having 2 to 10 carbon atoms, such as citric acid,are particularly preferred.

As previously shown in the Table 1, formic acid and oxalic acid do nothave a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV, and do not conform to thereducing agent of the present invention. However, derivatives of formicacid and oxalic acid, for example, their salts, may have a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV, and can conform to the reducing agent of thepresent invention.

As the derivative of the phenolic acid, a polyhydroxyaryl can be usedpreferably. As the polyhydroxyaryl, 1,2,3-trihydroxybenzene and1,4-dihydroxybenzene are preferred. As the derivatives of the organicacid, salts, esters, amides, and acid anhydrides are preferred. As thederivatives of hypophosphorous acid, salts and esters can be usedpreferably, and salts are particularly preferred.

A purification apparatus 1400 of the present embodiment is the same asthe embodiment shown in FIG. 18, except that a water soluble reducingagent is used as the reducing agent, and a reducing agent tank 1410 isprovided on the ground surface. The same elements as in FIG. 18 areassigned the same numerals in the 1400 range.

A reducing agent supply line C1 including a pump P is connected to areducing agent tank 1410. A nutrient solution supply line E1 including apump 1430 is connected to a nutrient solution tank 1440. In the presentembodiment, a line mixer M for connecting the reducing agent supply lineC1 and the nutrient solution supply line E1 is provided so that areducing agent and a nutrient solution are mixed there. However, theline mixer M may be omitted.

A purification method for a contaminated object, which uses thepurification apparatus 1400 of the present embodiment, is the same asthe purification method for a contaminated object using the purificationapparatus 1300, except that after the reducing agent and the nutrientsolution are mixed in the ground surface portion, the resulting mixtureis added to circulating water. That is, water introduced from an aquifer2 into a purification tank 1420 via a water intake portion 1422 of thepurification tank 1420 is pumped up by a lifting pump 1460 in thelongitudinal direction of the purification tank 1420, and returned intothe aquifer 2 via a water discharge portion 1421. At the ground surfaceportion, a water soluble reducing agent is supplied from the reducingagent tank 1410 to the line mixer M via the reducing agent supply lineC1, while a nutrient solution is supplied from the nutrient solutiontank 1440 to the line mixer M via the nutrient solution supply line E1.Thus, the reducing agent and the nutrient solution are mixed in the linemixer M. The mixed reducing agent and nutrient solution are introducedto a site below a line mixture 1470 inside the purification tank 1420via a purifying solution supply line C2. There, the reducing agent andnutrient solution are added to groundwater which is circulating. Thegroundwater incorporating the reducing agent and nutrient solution isgiven a reducing power and a nutrient source, and returned into theaquifer 2 via the water discharge portion 1421. Thus, the contaminatedobject can be purified by a reduction reaction and a biodegradationreaction. The line mixer 1470, for example, is not an essential elementand can be omitted.

Next, a sixteenth embodiment of the present invention is schematicallyshown in FIG. 21. A purification apparatus 1500 of the presentembodiment is effective when there is an obstacle, such as a plant,above contaminated soil and groundwater to be purified. The purificationapparatus 1500 is the same as the embodiment shown in FIG. 18, exceptthat a purification tank 1520 has a purification portion 1520 a locatedhorizontally in an aquifer 2, a first communication portion 1520 b forguiding a nutrient solution supply line E1, and a second communicationportion 1520 c. The same elements are assigned the same numerals in the1500 range for the purpose of illustration.

In the purification portion 1520 a of the purification tank 1520, astrainer portion 1522 constituting a water intake portion is formeddownstream with respect to groundwater, and a strainer portion 1521constituting a water discharge portion is formed upstream with respectto groundwater. The purification portion 1520 a of the purification tank1520 includes a submerged pump 1560 at a site close to the water intakepotion 1522, and a reducing agent tank 1510 at a site close to the waterdischarge potion 1521.

That is, the strainer portion 1522 for sucking in groundwater, pump1560, line mixer 1570, reducing agent tank 1510 for reducinggroundwater, and strainer portion 1521 for discharging the reducedgroundwater are provided in this order inside the purification tank1520. However, the reducing agent tank 1510 and the line mixer 1570 maybe installed in the reverse order. If groundwater can sufficientlycontact the reducing agent inside the reducing agent tank 1510,moreover, the line mixer 1570 can be omitted.

Supply of the nutrient solution is performed via the nutrient solutionsupply line E1 extending from a nutrient solution tank 1540 provided onthe ground surface. In the illustrated embodiment, the nutrient solutionsupply line E1 is guided by the first communication portion 1520 b ofthe purification tank 1520, but may be configured to be guided by thesecond communication portion 1520 c. When the nutrient solution issupplied via the first communication portion 1520 b, it is fed near thewater intake portion 1522. Thus, the nutrient solution is directly addedto the sucked-in groundwater, and then the reducing agent is added tothe groundwater containing the nutrient solution. When the nutrientsolution is supplied via the second communication portion 1520 c, it isfed near the water discharge portion 1521. Thus, the nutrient solutionis added after the reducing agent is added to the groundwater.

Purification of groundwater and soil by the purification apparatus 1500of the present embodiment is performed by repeating a process whichcomprises sucking in groundwater via the water intake portion 1522,flowing it longitudinally of the purification tank 1520 by the pump 1560as a reverse flow relative to the flow 90 of groundwater inside theaquifer 2, adding the nutrient solution, which has been supplied fromthe nutrient solution supply line E1, to the extracted groundwater,passing the mixture through the reducing agent tank 1510 to add thereducing agent, and returning the groundwater containing the nutrientsolution and the reducing agent from the water discharge portion 1521into the aquifer 2. That is, while groundwater is circulating in thepurification apparatus 1500, the nutrient solution and the reducingagent in the reducing agent tank 1510 are repeatedly added. Thegroundwater thus reduced and given the nutrient solution is circulated,whereby the soil can be purified repeatedly.

When the water intake portion 1522 is installed at a relativelylow-water level site, and the water discharge portion 1521 is installedat a relatively high water level site, the following advantage isproduced: The circulation speed is increased under the own weight of theions of the reducing agent contained in the groundwater flowing out ofthe water discharge portion 1521, in addition to the flow 90 ofgroundwater.

Further, a seventeenth embodiment of the present invention isschematically shown in FIG. 22. A purification apparatus 1600 of thepresent embodiment is the same as the sixteenth embodiment shown in FIG.21, except that a reducing agent tank 1610 is provided at a groundsurface portion. The same elements are assigned the same numerals in the1600 range for the purpose of illustration.

In the illustrated embodiment, the reducing agent tank 1610 accepts anutrient solution supply line E1 from a nutrient solution tank 1640 forholding a nutrient solution, and is connected to a purifying solutionsupply line C2 for introducing the nutrient solution and a reducingagent into a purification tank 1620. The purifying solution supply lineC2 is provided along a first connection portion 1620 b, and guides thenutrient solution and the reducing agent to a purification portion 1620a of the purification tank 1620.

Purification of the contaminated object by use of the purificationapparatus 1600 of the present embodiment is performed in the same manneras the purification method in the aforementioned sixteenth embodiment,except that the nutrient solution and the reducing agent are addedtogether to groundwater circulating between the purification portion1620 a and the aquifer 2.

In the embodiment of FIG. 22, the nutrient solution in the nutrientsolution tank 1640 provided on the ground surface is introduced into thereducing agent tank 1610 by a pump 1630. However, this order may bereversed. That is, the nutrient solution or a nutrient source may beadded to water which has been reduced by passing through the reducingagent tank. Such an embodiment is described, for example, in FIG. 29.

Next, an eighteenth embodiment of the present invention is schematicallyshown in FIG. 23. A purification apparatus 1700 of the presentembodiment is equipped with a purification tank 1720 which has a pumpingwell 1720 a having a strainer portion 1722 constituting a water intakeportion and a submerged pump 1760, and a pair of injection wells 1720 band 1720 c having water discharge portions, i.e., strainer portions 1721b and 1721 c; a reducing agent tank 1710 and a nutrient solution tank1740 provided in a ground surface portion; a groundwater supply line Wfor guiding groundwater sucked from the water intake portion 1722 to thereducing agent tank 1710; a reducing agent supply line C1 forintroducing groundwater containing a reducing agent from the reducingagent tank 1710 to the nutrient solution tank 1740; and a purifyingsolution supply line C2 for introducing the reducing agent and thenutrient solution from the nutrient solution tank 1740 into theinjection wells 1720 b and 1720 c of the purification tank 1720. Thepair of injection wells 1720 b and 1720 c having the water dischargeportions are located in a relatively high water level region of anaquifer 2, while the pumping well 1720 a having the water intake portionis located in a relatively low water level region of the aquifer 2.

In the eighteenth embodiment, purification of the contaminated object isperformed in the following manner:

Groundwater sucked via the water intake portion 1722 of the pumping well1720 a is pumped up by the pump 1760 to the reducing agent tank 1710 viathe groundwater supply line W. The pumped-up groundwater incorporatesthe reducing agent in the reducing agent tank 1710 and simultaneouslyundergoes a reducing action, and is then introduced into the nutrientsolution tank 1740 via the reducing agent supply line C1 to incorporatethe nutrient solution. Then, the groundwater is returned into theaquifer 2 through the water discharge portions 1721 b and 1721 c of theinjection wells 1720 b and 1720 c of the purification tank 1720 via thepurifying solution supply line C2. The nutrient solution arrives at acontaminated site 2 a around the pumping well 1720 a according to thewater level gradient of the aquifer 2.

The contaminated site 2 a is also purified by physical cleaning with thepurifying solution. Moreover, the purifying solution has a reducingaction, so that halogenated compounds in the contaminated object 2 a arealso degraded by a reduction reaction, i.e., a chemical reaction.Furthermore, the purifying solution contains the nutrient solution.Thus, microorganisms which degrade halogenated compounds grow, degradingthe halogenated compounds microbiologically.

In a place where the layer thickness of the aquifer 2 and the layerthickness of the vadose zone 1 are relatively large, the eighteenthembodiment can produce a particularly great water level gradient. Thus,the speed of circulation increases, and the purification efficiencyincreases. Moreover, the contaminated groundwater circulates between thepumping well 1720 a and the injection wells 1720 b, 1720 c, thuspreventing spread of the contaminated object. Furthermore, the locationsof installation of the injection wells 1720 b, 1720 c and pumping well1720 a can be changed according to the size of the contaminated site.

FIG. 24 shows a nineteenth embodiment of the present invention. Apurification apparatus 1800 in the present embodiment is the same as theeighteenth embodiment shown in FIG. 23, except that the order ofarrangement of a reducing agent tank 1810 and a nutrient solution tank1840 is reversed. In the eighteenth and nineteenth embodiments, areducing agent and a nutrient solution are circulated along withgroundwater. In such a case, as circulation proceeds, the importance oforder concerning which of the reducing agent and the nutrient solutionshould be added first is decreased.

The same elements will be assigned the same numerals in the 1800 rangefor purpose of illustration. Hereinbelow, an explanation for aconfiguration different from that in FIG. 23 will be offered, and thedescription of the same constitution will be omitted.

Groundwater sucked via a water intake portion 1822 of a pumping well1820 a is introduced by a pump 1860 to the nutrient solution tank 1840via a groundwater supply line W to incorporate a nutrient solution.Then, the groundwater is introduced into the reducing agent tank 1810via a nutrient solution supply line E1 to incorporate a reducing agentin the reducing agent tank 1810 and simultaneously undergo a reducingaction. Then, the reduced groundwater is returned into the aquifer 2through water discharge portions 1821 b and 1821 c of injection wells1820 b and 1820 c of a purification tank 1820 via a purifying solutionsupply line C2.

In the eighteenth and nineteenth embodiments shown in FIGS. 23 and 24,the use of a solid reducing agent is shown. When a water solublereducing agent is used, a reducing agent tank and a line mixer M asillustrated in FIG. 20 may be used in place of the reducing agent tanks1710 and 1810.

In the embodiments shown in FIGS. 23 and 24, the pair of injection wellsare used. However, the number of the injection wells is not limited, andthere may be one, two or more, for example, three or more of theinjection wells. Similarly, the number of the pumping wells is notlimited, and there may be one, two or more, for example, three or moreof the pumping wells. For example, two or more of the pumping wells andone or more of the injection wells may be used. Alternatively, onepumping well and one or more injection wells may be used.

Nor is the positional relationship between the pumping well and theinjection well restricted. As shown in FIGS. 23 and 24, the pumping wellmay be disposed between two or more of the injection wells. Conversely,the injection well may be disposed between two or more of the pumpingwells.

Furthermore, three or more of the injection wells may be arranged so asto surround one or more of the pumping wells. Conversely, three or moreof the pumping wells may be arranged so as to surround one or more ofthe injection wells. Here, the description “three or more” is given,because it is difficult to say that “two” wells surround the equivalentwells.

FIGS. 25 and 26 show a twentieth embodiment and a twenty-firstembodiment, respectively. In each case, groundwater is circulated usingone injection well and one pumping well. The same elements are indicatedby the equivalent numerals in the 1900 range and the 2000 range,respectively, and explanations are omitted, where necessary.Purification apparatuses 1900 and 2000 shown in FIGS. 25 and 26 areeffective particularly when there is an obstacle, such as a plant, onthe soil containing a contaminated object to be purified.

In FIG. 25, ground water sucked via a water intake portion 1922 of apumping well 1920 a is introduced by a pump 1960 to a reducing agenttank 1910 via a groundwater supply line W. The groundwater undergoes areducing action by a reducing agent in the reducing agent tank 1910, andis then introduced into a nutrient solution tank 1940 via a line C1 toincorporate a nutrient solution. The groundwater having the nutrientsolution added is returned into an aquifer 2 by a pump 1930 through awater discharge portion 1921 of an injection well 1920 via a purifyingsolution supply line C2. In the aquifer 2, the purifying solutionarrives at a contaminated site 2 a along the flow 90 of groundwater.

The contaminated site 2 a is also purified by physical cleaning with thepurifying solution. Moreover, the purifying solution has a reducingaction, so that halogenated compounds in the contaminated object 2 a arealso degraded by a reduction reaction, i.e., a chemical reaction.Furthermore, the purifying solution contains the nutrient solution.Thus, microorganisms which degrade halogenated compounds grow, degradingthe halogenated compounds microbiologically.

The twenty-first embodiment of the present invention shown in FIG. 26 isthe same as the twentieth embodiment shown in FIG. 25, except that theorder of arrangement of a reducing agent tank 2010 and a nutrientsolution tank 2040 is reversed. In the twentieth and twenty-firstembodiments, a reducing agent and a nutrient solution are circulatedalong with groundwater. In such a case, as circulation proceeds, theimportance of order concerning which of the reducing agent and thenutrient solution should be added first is decreased.

Next, twenty-second and twenty-third embodiments using a pair ofunderground walls instead of a pair of wells are shown in FIGS. 27 and28. The purification apparatuses of these embodiments are the same asthe embodiments shown in FIGS. 25 and 26, except that the undergroundwalls are used. The same elements are indicated by the equivalentnumerals in the 2100 and 2200 ranges, respectively, and explanations forthe same constituent elements are omitted. The underground wall refersto something like a well extending laterally to form a wall underground.The underground wall comprises an open end portion, a deep groove dug inthe ground, and a bottom portion. Inside the deep groove, an elementwith high permeability to air and liquid, typically such as sand orgravel, is buried to prevent collapse of the groove. The deep groove ofthe underground wall forms a side wall of the underground wall, and isformed with a deposition of the element having excellent air and liquidpermeability. Thus, the entire wall surface exhibits the same functionas that of a strainer portion.

In a purification apparatus 2100, one of underground walls, 2120 a, actsas a water intake portion, and the other underground wall 2120 b acts asa water discharge portion. The entire wall surface of the undergroundwall exhibits the same function as that of a strainer portion as statedabove. Thus, groundwater can be taken in from any part of the wallsurface, and a nutrient solution and a reducing agent can be added inlarge amounts. The use of the underground wall brings the advantage thatwhen a great water level gradient cannot be formed because of the highwater level of the groundwater of the aquifer 2 or the small thicknessof the aquifer, the reducing agent and the nutrient solution can bediffused in a horizontally broad range.

A contaminated site 2 a is also purified by physical cleaning with thepurifying solution. Moreover, the purifying solution has a reducingaction, so that halogenated compounds in the contaminated object 2 a arealso degraded by a reduction reaction, i.e., a chemical reaction.Furthermore, the purifying solution contains the nutrient solution.Thus, microorganisms which degrade halogenated compounds grow, degradingthe halogenated compounds microbiologically.

Next, another embodiment of the present invention is shown in FIGS. 29and 30. The embodiment shown in FIGS. 29 and 30 is not of thecirculation type involving the circulation of groundwater, but isdesigned to add a reducing agent and a nutrient to an aquifer 2.

A purification apparatus 2300 shown in FIG. 29 has a reducing agent tank2310, a nutrient solution tank 2340 for preparing a nutrient solutionaccording to the properties of microorganisms in a contaminated objectto be purified, and a purification tank 2320. A water supply line W1 forsupplying water from a water tank T, and a reducing agent supply line C1for supplying the nutrient solution tank 2340 with water containing areducing agent are connected to the reducing agent tank 2310. A nutrientsolution supply line E1 for supplying a reduced nutrient solution to thepurification tank 2320 is connected to the nutrient solution tank 2340.In a lower part of the purification tank 2320, a strainer portion 2321is provided for allowing the supplied reducing agent and nutrientsolution to permeate the contaminated object. The purification tank 2320is installed underground so that the strainer portion 2321 will belocated in the underground aquifer 2.

For the reducing agent tank 2310, the water supply line W1 may beconnected to a top portion 2310 a of the reducing agent tank 2310 asshown in FIG. 30, or the water supply line W1 may be connected to abottom portion 1310 b of the reducing agent tank 1310 as shown in FIG.19.

A reducing agent tank 2410 shown in FIG. 30 includes a support floor2411 provided in a lower part thereof, a solid reducing agent contactportion 2412 supported by the support floor 2411, a first gap portion2413 above the solid reducing agent contact portion 2412, and a secondgap portion 2414 below the solid reducing agent contact portion 2412.The solid reducing agent contact portion 2412 includes a support mediumsuch as gravel, and the solid reducing agent carried on the medium. Thesolid reducing agent is, for example, a powder measuring 500 μm or less.The support floor 2411 has many small holes of a size enough to allowpassage of water, but allow no passage of the solid reducing agent. Thesupport floor is, for example, a plate-like member composed of stainlesssteel. The first gap portion 2413 and the second gap portion 2414 are ofa sufficient size for water fed from the water supply line W1 to flowinto the solid reducing agent contact portion 2412 constantly at adesired speed.

When the water supply line W1 is connected to the top portion 2410 a ofthe reducing agent tank 2410, as shown in FIGS. 29 and 30, water fed tothe top portion 2410 a of the reducing agent tank 2410 flows through thesolid reducing agent contact portion 2412 by its own weight, and isreduced thereby. When the water supply line W is connected to the bottomportion 1310 b of the reducing agent tank 1310, as shown in FIG. 19,water needs to be forcibly sucked by a pump or the like provided on thereducing agent supply line C1 connected to the top portion 1310 a of thereducing agent tank 1310.

It is also possible to provide a three-valve valve V1 in the reducingagent supply line C1 and connect a backwash water flow line PL via thethree-way valve V1, as shown in FIG. 30. In this case, cleaning water ispassed through the interior of the reducing agent tank 2410 from belowto above via the backwash water flow line PL, whereby the solid reducingagent contact portion 2412 can be backwashed. As a result, clogging ofthe solid reducing agent contact portion 2412 and the pores of thesupport floor 2411 can be prevented.

A purification method for a contaminated object, such as groundwater orsoil, contaminated with halogenated organic compounds, the purificationmethod using the purification apparatus 2400 of the present embodiment,includes a water reduction step in which a reducing agent having astandard electrode potential, relative to a standard hydrogen electrodeat 25° C., of 300 mV to −2400 mV reduces water; a nutrient solutionreduction step of adding water reduced in the reduction step to anutrient solution containing a nutrient source for heterotrophicanaerobic microorganisms to reduce the nutrient solution; and a step ofadding the nutrient solution reduced in the nutrient solution reductionstep to the contaminated object. The water reduction step is performedinside the reducing agent tank 2410, while the nutrient solutionreduction step is performed inside the nutrient solution tank 2340. Theamount of water added to the reducing agent tank 2410 is not restricted,and can be set arbitrarily in such a range as to avoid the situationthat the groundwater level near the well rises to reach the surface ofthe earth.

In detail, water is supplied from the water tank T to the reducing agenttank 2410 via the water supply line W1. The supplied water contacts thereducing agent while passing through the reducing agent tank 2410, andis reduced thereby, or dissolves the reducing agent and incorporates it.The thus reduced water is supplied to the nutrient solution tank 2340via the reducing agent supply line C1. Then, the reduced water and watercontaining the reducing agent contacts the nutrient solution in thenutrient solution tank 2340 to reduce the nutrient solution. The reducednutrient solution is supplied into the purification tank 2320 by aninjection pump 2330 via a purifying solution supply line C2. The reducednutrient solution permeates the contaminated object via the strainerportion 2321 formed in the lower part of the purification tank 2320. Asa result, the reduced nutrient solution reacts with the halogenatedorganic substances contained in the contaminated object to dehalogenatethem, and simultaneously enhances the activity of the heterotrophicanaerobic microorganisms present in the contaminated object to promote abiodegradation reaction by the microorganisms, thereby purifying thecontaminated object.

Next, still another embodiment of the present invention is schematicallyshown in FIG. 31. The embodiment shown in FIG. 31 is in the sameconfiguration as the embodiment shown in FIG. 29, except that thepurification tank is laid horizontally in the aquifer 2. The sameelements are indicated by the equivalent numerals in the 2500 range.

In a purification apparatus 2500 of the present embodiment, apurification tank 2520 has a pair of inclined portions, 2520 b and 2520c, and a purification portion 2520 a having a strainer portion 2521lying horizontally in the aquifer 2. The first inclined portion 2520 baccepts a reduced nutrient solution via a purifying solution supply lineC2. The strainer portion 2521 is located horizontally in the aquifer 2,and allows the reduced nutrient solution to pass into the aquifer 2. Thesecond inclined portion 2520 d has a closed end protruding from theground surface.

In FIG. 31, the strainer portion 2521 extends horizontally, but thestrainer portion may be inclined. Depending on the method of formation,the second inclined portion 2520 c can be omitted.

A purification method for the contaminated object, which uses thepurification apparatus 2500 of the present embodiment, is the same asthe embodiment shown in FIG. 29, except that the reduced nutrientsolution flows out vertically from the strainer portion 2521. Thepurification apparatus 2500 and purification method of the presentembodiment are effective when there is a building, such as a plant, onthe ground surface directly above groundwater or soil including acontaminated object to be purified.

Even in the embodiments shown in FIGS. 29 and 31, not only a solidreducing agent, but also a water soluble reducing agent can be used asthe reducing agent.

According to a purification apparatus and a purification method as otheraspects of the present invention, a contaminated object containinghalogenated organic compounds can be purified efficiently and easily.Particularly, water is reduced while being circulated between a sitefilled with flowable water in the contaminated object and thepurification apparatus; for example, in the above-described embodiment,groundwater being circulated between the aquifer 2 and the purificationapparatus. By this measure, water dehalogenated and given a reducingpower can be returned into the contaminated object, without a rapidchange in the quality of water, whereby the halogen ion concentration inthe contaminated object can be decreased gradually, and the contaminatedobject containing halogenated organic compounds can be purifiedsatisfactorily. Also, by giving the nutrient solution in a reducedstate, the activity of heterotrophic microorganisms can be enhanced.Consequently, the contaminated object containing halogenated organiccompounds can be purified satisfactorily by a combination of a chemicalreaction and a biodegradation reaction.

Furthermore, according to a purification apparatus and a purificationmethod as other aspects of the present invention, a contaminated objectcontaining halogenated organic compounds can be purified easily andcontinuously in situ.

FIG. 32 shows another embodiment of a purification apparatus of thepresent invention. A shallow groove such as a trench, or an indentation,2610, is dug in the ground surface. A groove is relatively narrow inwidth in comparison with a dimension in a direction in which the grooveextends. On the other hand, an indentation may be narrow or broad inwidth. That is, a trench or groove is included in an indentation.

A reducing agent 2620, preferably a solid reducing agent, is filled as afirst layer into a lower part of the indentation, and a nutrient source2630, preferably a solid nutrient source, for heterotrophic anaerobicmicroorganisms is filled as a second layer into an upper part of theindentation. The indentation is provided above or upstream from acontaminated object 2602 containing halogenated organic compounds in thesoil. Groundwater pumped up from the aquifer, or tap water may besprinkled over the nutrient source 2630 via a line 2640. Alternatively,rainwater may be allowed to flow into the nutrient source 2630, withoutperforming such sprinkling. In the case of groundwater, groundwater maybe extracted from a pumping well having a strainer portion, or anunderground wall, by a pump or the like, as stated earlier.

As a result, the sprinkled water or the rainwater passes through thenutrient source, turning into water containing the nutrient source. Thatis, a nutrient solution containing the nutrient source for heterotrophicanaerobic microorganisms and water is formed. Then, this nutrientsolution is reduced with the reducing agent 2620. The reduced nutrientsolution seeps into the soil by gravity, and is introduced into thecontaminated object in the soil to purify the contaminated object.

A solid nutrient source is preferred as the nutrient source. As thesolid nutrient source, it is preferred to use a solid organic materialsuch as compost, manure, excess sludge, sediment with a high organicmatter content, or organic waste. The solid nutrient source covers thereducing agent, and thus can decrease the contact of the reducing agentwith oxygen in the air. Because of this arrangement, the reducing agentcan be prevented from being consumed by reducing oxygen in the air.

Alternatively, it is permissible to provide a pumping well downstreamfrom the contaminated object 2602, extract groundwater from this pumpingwell, and sprinkle groundwater over the nutrient source 2630 via theline 2604.

In FIG. 32, the indentation 2610 is formed at a lower level than aground surface 2604. However, the indentation may be formed at a higherlevel than the ground surface 2604.

FIG. 33 shows another embodiment of the present invention. In order toform an indentation 2710, a protuberance 2712 is formed around a portion2710 which will become the indentation 2710. The bottom 2714 of theindentation 2710 may be nearly on the same plane as a ground surface2704, or may be at a higher or lower level than the ground surface 2704.

A reducing agent 2720, preferably a solid reducing agent, is filled as afirst layer into a lower part of the indentation 2710, and a nutrientsource 2730, preferably a solid nutrient source, for heterotrophicanaerobic microorganisms is filled as a second layer into an upper partof the indentation. Groundwater pumped up from the aquifer, or tap watermay be sprinkled over the nutrient source 2730 via a line 2740.Alternatively, rainwater may be allowed to flow into the nutrient source2730, without performing such sprinkling.

As a result, the sprinkled water or the rainwater passes through thenutrient source, turning into water containing the nutrient source. Thatis, a nutrient solution containing the nutrient source for heterotrophicanaerobic microorganisms and water is formed. Then, this nutrientsolution is reduced with the reducing agent 2720. The reduced nutrientsolution seeps into the soil by gravity, and is introduced into thecontaminated object in the soil to purify the contaminated object.

The protuberance 2712 may be arranged repeatedly, whereby a plurality ofthe indentations 2710 may be formed repeatedly. The shape of the bottomsurface of the indentation is not restricted, and may be quadrilateralor circular.

Alternatively, it is permissible to provide a pumping well downstreamfrom a contaminated object 2702 with respect to the flow of groundwater,extract groundwater from this pumping well, and sprinkle groundwaterover the nutrient source 2730 via the line 2704.

In the embodiments of FIGS. 32 and 33, particularly when the line isomitted, the contaminated object can be naturally purified each time therain falls, and a power of a pump or the like is unnecessary.

What is claimed is:
 1. A purification method for purifying acontaminated object containing halogenated organic compounds, including:a reduction step in which a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of 300mV to −2400 mV reduces a nutrient solution containing a nutrient sourcefor heterotrophic anaerobic microorganisms and water; and anintroduction step of introducing the reduced nutrient solution into thecontaminated object after the reduction step.
 2. The purification methodas claimed in claim 1, wherein a well, an underground wall, a permeationgutter, a trench, or an indentation is used in the introduction step. 3.A purification method for purifying a contaminated object containinghalogenated organic compounds, including: a water reduction step ofreducing water with a reducing agent having a standard electrodepotential, relative to a standard hydrogen electrode at 25° C., of 300mV to −2400 mV; a contact step of bringing the water reduced in thereduction step into a nutrient source for heterotrophic anaerobicmicroorganisms to obtain a mixture containing the nutrient source; andan addition step of adding the mixture obtained in the contact step tothe contaminated object.
 4. The purification method as claimed in claim3, wherein a well, an underground wall, a permeation gutter, a trench,or an indentation is used in the water reduction step, the contact step,or the addition step.
 5. A purification method for purifying acontaminated object containing halogenated organic compounds, including:a circulation step of circulating water so as to pass through thecontaminated object; and a reduction step of reducing the circulatingwater with a reducing agent having a standard electrode potential,relative to a standard hydrogen electrode at 25° C., of 300 mV to −2400mV.
 6. The purification method as claimed in claim 5, wherein thereduction step is performed in soil.
 7. The purification method asclaimed in claim 5, wherein the circulation step has a step of taking inwater present in the soil, and a step of discharging water into thesoil.
 8. The purification method as claimed in claim 7, wherein a well,an underground wall, a permeation gutter, a trench, or an indentation isused in the step of taking in water present in the soil.
 9. Thepurification method as claimed in claim 7, wherein a well, anunderground wall, a permeation gutter, a trench, or an indentation isused in the step of discharging water into the soil.
 10. Thepurification method as claimed in claim 5, wherein the reduction step isperformed by the reducing agent which is in a solid state, and insolubleor sparingly soluble in water.
 11. The purification method as claimed inclaim 5, wherein the reduction step is performed by the reducing agentwhich is water soluble.
 12. The purification method as claimed in claim5, having a nutrient source contact step of further bringing a nutrientsource for heterotrophic anaerobic microorganisms into contact withwater before being circulated.
 13. The purification method as claimed inclaim 5, having a nutrient source contact step of further bringing anutrient source for heterotrophic anaerobic microorganisms into contactwith water being circulated.
 14. A purification apparatus for purifyinga contaminated object containing halogenated organic compounds,comprising: reduction means by which a reducing agent having a standardelectrode potential, relative to a standard hydrogen electrode at 25°C., of 300 mV to −2400 mV reduces a nutrient solution containing anutrient source for heterotrophic anaerobic microorganisms and water;and introduction means by which the reduced nutrient solution isintroduced into the contaminated object via an introduction portion forintroducing the reduced nutrient solution into the contaminated object.15. The purification apparatus as claimed in claim 14, wherein thereduction means includes a contact device for bringing the nutrientsolution into contact with the reducing agent which is in a solid stateand is insoluble or sparingly soluble in water.
 16. The purificationapparatus as claimed in claim 14, wherein the reduction means includes amixing device for mixing the nutrient solution with an aqueous solutioncontaining the reducing agent which is water soluble.
 17. Thepurification apparatus as claimed in claim 14, wherein the reductionmeans includes an underground wall filled with a water permeable filler,and the reducing agent is used as at least a part of the filler.
 18. Thepurification apparatus as claimed in claim 14, further having pumpingmeans for introducing the contaminated object into the introductionportion to perform circulation treatment of the contaminated object. 19.The purification apparatus as claimed in claim 14, wherein theintroduction portion has a well, an underground wall, a permeationgutter, a trench, or an indentation.
 20. The purification apparatus asclaimed in claim 14, wherein the introduction means has a pump.
 21. Apurification apparatus for purifying a contaminated object containinghalogenated organic compounds, characterized by having: a reducing agenthaving a standard electrode potential, relative to a standard hydrogenelectrode at 25° C., of 300 mV to −2400 mV; a water intake portionlocated in the contaminated object or downstream from the contaminatedobject; and a water discharge portion located upstream from the waterintake portion and located in the contaminated object or upstream fromthe contaminated object, and characterized in that water is circulatedamong the water intake portion, the reducing agent, and the waterdischarge portion to purify the contaminated object.
 22. Thepurification apparatus as claimed in claim 21, wherein the reducingagent includes a reducing agent which is in a solid state and insolubleor sparingly soluble in water.
 23. The purification apparatus as claimedin claim 21, wherein the reducing agent includes a water solublereducing agent.
 24. The purification apparatus as claimed in claim 21,wherein the reducing agent is located between the water intake portionand the water discharge portion.
 25. The purification apparatus asclaimed in claim 21, wherein the reducing agent is held in a reducingagent tank.
 26. The purification apparatus as claimed in claim 21,wherein the water intake portion or the water discharge portion isprovided in a well, an underground wall, a permeation gutter, a trench,or an indentation.
 27. The purification apparatus as claimed in claim21, having a pump in relation to circulation of water.
 28. Thepurification apparatus as claimed in claim 21, further having a nutrientsource for heterotrophic anaerobic microorganisms.
 29. The purificationapparatus as claimed in claim 28, wherein water before being circulatedis contacted with the nutrient source.
 30. The purification apparatus asclaimed in claim 28, wherein water is circulated among the water intakeportion, the reducing agent, the nutrient source, and the waterdischarge portion to purify the contaminated object.
 31. Thepurification apparatus as claimed in claim 28, further having a nutrientsource tank holding the nutrient source.
 32. A purification apparatusfor purifying contaminated soil containing halogenated organiccompounds, including: an indentation formed in a ground surface above orupstream from the contaminated soil; a reducing agent disposed in theindentation and having a standard electrode potential, relative to astandard hydrogen electrode at 25° C., of 300 mV to −2400 mV; and anutrient source for heterotrophic anaerobic microorganisms which isdisposed above the reducing agent.
 33. The purification apparatus asclaimed in claim 32, wherein the reducing agent is a solid.
 34. Thepurification apparatus as claimed in claim 32, wherein the nutrientsource is a solid.
 35. The purification apparatus as claimed in claim32, wherein the reducing agent and the nutrient source are each arrangedin a layer, and the layer comprising the nutrient source covers thelayer comprising the reducing agent.